Online Etymology Dictionary

tessera (n.): plural tesserae, "small, square piece of stone," 1650s, from Latin tessera "a die, cube, square tablet with writing on it" used as a token or ticket, from Ionic Greek tessera, neuter of tesseres (Attic tessares) "four" (see four).
tesseract (n.): "four-dimensional 'cube,'" 1888, from tessera + Greek aktis "ray" (see actino-).
test (n.): late 14c., "small vessel used in assaying precious metals," from Old French test, from Latin testum "earthen pot," related to testa "piece of burned clay, earthen pot, shell" (see tete).

Sense of "trial or examination to determine the correctness of something" is recorded from 1590s. The connecting notion is "ascertaining the quality of a metal by melting it in a pot." Test Act was the name given to various laws in English history meant to exclude Catholics and Nonconformists from office, especially that of 1673, repealed 1828. Test drive (v.) is first recorded 1954.
test (v.): 1748, "to examine the correctness of," from test (n.), on the notion of "put to the proof." Earlier "assay gold or silver" in a test (c. 1600). Meaning "to administer a test" is from 1939; sense of "undergo a test" is from 1934. Related: Tested; testing.
test-tube (n.): 1809, from test (n.) + tube (n.). So called because it originally was used to test the properties of liquids. Test-tube baby is recorded from 1935.
testament (n.): late 13c., "last will disposing of property," from Latin testamentum "a last will, publication of a will," from testari "make a will, be witness to," from testis "witness," from PIE *tri-st-i- "third person standing by," from root *tris- "three" (see three) on the notion of "third person, disinterested witness."

Use in reference to the two divisions of the Bible (early 14c.) is from Late Latin vetus testamentum and novum testamentum, loan-translations of Greek palaia diatheke and kaine diatheke. Late Latin testamentum in this case was a confusion of the two meanings of Greek diatheke, which meant both "covenant, dispensation" and "will, testament," and was used in the former sense in the account of the Last Supper (see testimony) but subsequently was interpreted as Christ's "last will."
testamentary (adj.): "pertaining to a will or wills," mid-15c., from Latin testamentarius, from testamentum (see testament).
testate (adj.): "having left a valid will," late 15c., from Latin testatus "public, manifest, published," past participle of testari "make a will, be witness to, declare" (see testament).
testator (n.): c. 1400, from Anglo-French testatour (c. 1300), from Late Latin testator "one who makes a will," from testari (see testate). Fem. form testatrix is attested from 1590s.
tester (n.1): "one who tests, puts to trial, or assays," 1660s, agent noun from test (v.). Earlier "a crucible" for trying metals by heating them (mid-15c.).
tester (n.2): "canopy over a four-post bed," mid-14c., from Medieval Latin testerium, from testera "head-stall" of the bridle of a horse, extended use and form of Late Latin testa "skull," in Vulgar Latin "head" (see tete). From Medieval Latin testa as "head" also come tester in obsolete senses of "piece of armor for the head" (late 14c., via Old French testiere) and "coin of Henry VIII" (1546), the first English coin to bear a true portrait.
testes (n.): see testis.
testicle (n.): early 15c., alteration of testicule (late 14c.), from Latin testiculus, diminutive of testis "testicle" (see testis). Old English had beallucas (see ballocks) and herþan, probably originally "leather bag" (compare heorþa "deer-skin"). The commonest slang terms for them in other languages are words that mean "balls," "stones," "nuts," "eggs."
testicular (adj.): 1650s, from Latin testiculus (see testicle) + -ar.
testify (v.): late 14c., "give legal testimony, affirm the truth of, bear witness to;" of things, c. 1400, "serve as evidence of," from Anglo-French testifier, from Latin testificari "bear witness, show, demonstrate," also "call to witness," from testis "a witness" (see testament) + root of facere "to make" (see factitious). Biblical sense of "openly profess one's faith and devotion" is attested from 1520s. Related: Testified; testifying; testification.
testimonial (adj.): early 15c., "of or pertaining to testimony," in part from testimonial (n.) and from Late Latin testimonialis, from Latin testimonium (see testimony). Originally especially in phrase letters testimonial (Middle French lettres testimoniaulx, Latin litteræ testimoniales) "document or documents attesting to a fact or to the good standing of the bearer," literally "letters serving for evidence."
testimonial (n.): "statement, declaration," also "writing testifying to one's qualification or character," early 15c. (from Old French testimonial, variant of tesmoignal), short for letters testimonial (see testimonial (adj.)). Meaning "gift presented as an expression of appreciation" is from 1838.
testimony (n.): c. 1400, "proof or demonstration of some fact, evidence, piece of evidence;" early 15c., "legal testimony, sworn statement of a witness," from Old North French testimonie (Old French testimoine 11c.), from Latin testimonium "evidence, proof, witness, attestation," from testis "a witness, one who attests" (see testament) + -monium, suffix signifying action, state, condition. Despite the common modern assertion, the sense of the word is unlikely to have anything to do with testicles (see testis).

Earliest attested sense in English is "the Ten Commandments" (late 14c.), from Vulgate use of Late Latin testimonium, along with Greek to martyrion (Septuagint), translations of Hebrew 'eduth "attestation, testimony" (of the Decalogue), from 'ed "witness."
testis (n.): (plural testes), 1704, from Latin testis "testicle," usually regarded as a special application of testis "witness" (see testament), presumably because it "bears witness to male virility" [Barnhart]. Stories that trace the use of the Latin word to some supposed swearing-in ceremony are modern and groundless.

Compare Greek parastatai "testicles," from parastates "one that stands by;" and French slang témoins, literally "witnesses." But Buck thinks Greek parastatai "testicles" has been wrongly associated with the legal sense of parastates "supporter, defender" and suggests instead parastatai in the sense of twin "supporting pillars, props of a mast," etc. Or it might be a euphemistic use of the word in the sense "comrades." OED, meanwhile, points to Walde's suggestion of a connection between testis and testa "pot, shell, etc." (see tete).
testosterone (n.): male sex hormone, 1935, from German Testosteron (1935), coined from a presumed comb. form of Latin testis "testicle" (see testis) + first syllable of sterol + chemical ending -one.
testy (adj.): early 15c., "impetuous, rash," altered from Middle English testif "headstrong" (late 14c.), from Anglo-French testif, Old French testu (Modern French têtu) "stubborn, headstrong, obstinate," literally "heady," from teste "head" (see tete). Meaning "easily irritated, irascible" is first recorded 1520s. Related: Testily; testiness.
Tet (n.): Vietnamese lunar new year, 1885, short for Tet Nguyen Dan "feast of the first day." The North Vietnamese Tet Offensive in the U.S. Vietnam War began Jan. 30, 1968.
tetanus (n.): infectious disease, late 14c., from Latin tetanus "tetanus," from Greek tetanos "tetanus, muscular spasm," literally "a stretching, tension," from teinein "to stretch" (see tenet); "so called because the disease is characterized by violent spasms and stiffness of the muscles" [Barnhart]. Related: Tetanoid (adj.).
tetany (n.): 1890, from French tétanie "intermitent tetanus," from Modern Latin tetania (see tetanus).
tetched (adj.): 1930, U.S. colloquial variant of touched in the sense of "slightly crazy" (see touch (v.)).
tetchy (adj.): "easily irritated," 1592, teachie, in "Romeo & Juliet" I.iii.32; of uncertain origin. Perhaps from Middle English tatch "a mark, quality," derived via Old French from Vulgar Latin *tecca, from a Germanic source akin to Old English tacen (see token).
tete (n.): as a type of women's tall dressed hair or wig, 1756, from French tête "head," Old French teste, from Latin testa, literally "piece of earthenware, tile, potsherd; earthen pot, pitcher, jug; shell of shellfish," related to Latin testudo "tortoise" and texere "to weave" (compare Lithuanian tištas "vessel made of willow twigs;" see texture (n.)).

The "head" sense arose in Vulgar Latin, perhaps as a humorous use of the "jug, pot" meaning, or via Late Latin use of testa as "skull," from testa (capitis) "shell (of the head)." Compare German Kopf "head" from the root of English cup (n.).
tete-a-tete (n.): "a private meeting," from French tête-à-tête, literally "head-to-head," from Old French teste "head" (see tete). The adjective, "private, confidential, with none present but the persons concerned" is recorded from 1728; as an adverb from 1790.
tether (n.): late 14c., "rope for fastening an animal," not found in Old English, probably from a Scandinavian source akin to Old Norse tjoðr "tether," from Proto-Germanic *teudran (source also of Danish tøir, Old Swedish tiuther, Swedish tjuder, Old Frisian tiader, Middle Dutch tuder, Dutch tuier "line, rope," Old High German zeotar "pole of a cart"), from PIE root *deu- "to fasten" + instrumentive suffix *-tro-. Figurative sense of "measure of one's limitations" is attested from 1570s.
tether (v.): late 14c. (implied in tethering), "confine by a tether," originally of grazing animals, from tether (n.). Figurative use also from late 14c. Related: Tethered.
tetherball (n.): also tether-ball, 1900, from tether (n.) + ball (n.1).
Tethys: name for the sea that anciently lay between Eurasia and Africa-Arabia, coined 1893 by German geologist Eduard Suess (1831-1914), from Tethys, name of a Greek sea goddess, sister and consort of Oceanus.
Teton (n.): member of a western Sioux people, 1806, from Dakota titonwan, literally "dwellers on the prairie," from thi + huwa. Not related to the Grand Teton mountain range.
tetra-: before vowels tetr-, word-forming element meaning "four," from Greek tetra-, combining form of tettares (Attic), tessares "the numeral four" (see four).
tetracycline (n.): 1952, with chemical suffix -ine (2) + tetracyclic "containing four fused hydrocarbon rings," from tetra- + cyclic (see cycle (n.)).
tetrad (n.): "the number four, collection of four things," 1650s, from Greek tetras (comb. form tetrad-) "group of four, number four" (see tetra-).
tetragrammaton (n.): c. 1400, from Greek (to) tetragrammaton "(the word) of four letters," from tetra- "four" (see four) + gramma (genitive grammatos) "letter, something written" (see -gram). The Hebrew divine name, transliterated as YHWH, usually vocalized in English as "Jehovah" or "Yahweh."
tetrahedron (n.): "triangular pyramid, solid figure contained by four triangular surfaces," 1560s, from Late Greek tetraedron, noun use of neuter of tetraedros (adj.) "four-sided," from tetra- "four" (see tetra-) + hedra "seat, base, chair, face of a geometric solid," from PIE root *sed- (1) "to sit" (see sedentary). Related: Tetrahedral.
tetralogy (n.): 1650s, from Greek tetralogia, from tetra- (see tetra-) + -logia (see -logy). A group of four dramatic compositions, originally three tragedies (the trilogia) and a Satyric play.
tetrameter (n.): 1610s, from Late Latin tetrametrus, from Greek tetrametron "verse of four measures" (generally trochaic), noun use of neuter of tetrametros (adj.) "having four measures," from tetra- "four" (see tetra-) + metron "measure" (see meter (n.2)).
tetrapod (n.): "four-footed animal, quadruped," 1826, from Modern Latin tetrapodus, from Greek tetrapous "four-footed," as a noun, "four-footed animal," from tetra- (see tetra-) + pous "foot," from PIE root *ped- (1) "a foot" (see foot n.)).
tetrarch (n.): late Old English tetrarche "ruler of one of four divisions of a kingdom or province," from Late Latin tetrarcha, from tetrarches, from Greek tetrarkhes "leader of four companies, ruler of four provinces," from tetra- "four" (see tetra-) + arkhein "to rule" (see archon). Applied generally to subordinate rulers in the Roman Empire, especially in Syria. Related: Tetrarchy.
tetter (n.): skin disease, Old English teter, from a reduplicated form of PIE *der- (2) "to split, peel, flay" (see tear (v.1)).
Teuton (n.): "a German," 1833, in modern use often in contrast to Celt, probably a back-formation from Teutonic.
Teutonic (adj.): 1610s, "of or pertaining to the Germanic languages and to peoples or tribes who speak or spoke them," from Latin Teutonicus, from Teutones, Teutoni, name of a tribe that inhabited coastal Germany near the mouth of the Elbe and devastated Gaul 113-101 B.C.E., probably via Celtic from Proto-Germanic *theudanoz, from PIE *teuta-, the common word for "people, tribe" (source also of Lithuanian tauto, Oscan touto, Old Irish tuath, Gothic þiuda, Old English þeod "people, race, nation").

Used in English in anthropology to avoid the modern political association of German; but in this anthropological sense French uses germanique and German uses germanisch, because neither uses its form of German for the narrower national meaning (compare French allemand, for which see Alemanni; and German deutsch, under Dutch). In Finnish, Germany is Saksa "Land of the Saxons."

The Teutonic Knights (founded c.1191) were a military order of German knights formed for service in the Holy Land, but who later crusaded in then-pagan Prussia and Lithuania. The Teutonic cross (1882) was the badge of the order.
Tex: nickname for a Texan, by 1903, from Texas.
Tex-Mex (adj.): by 1914, from Texas + Mexico. An earlier noun for "Texan of Mexican background" was Texican (1863).
Texas: Mexican province, briefly an independent nation and now a U.S. state, from Spanish Texas, Tejas, earlier pronounced "ta-shas," originally an ethnic name, from Caddo (eastern Texas Indian tribe) taysha "friends, allies," written by the Spanish as a plural. Related: Texan. Baseball Texas-leaguer "ball popped up just over the head of the infielders and falling too close for outfielders to catch" is recorded from 1905, named for the minor league that operated in Texas from 1902 (one theory is that outfielders played unusually deep in Texas because hit balls bounced hard off the hard, sun-baked ground).
text (n.): late 14c., "wording of anything written," from Old French texte, Old North French tixte "text, book; Gospels" (12c.), from Medieval Latin textus "the Scriptures, text, treatise," in Late Latin "written account, content, characters used in a document," from Latin textus "style or texture of a work," literally "thing woven," from past participle stem of texere "to weave, to join, fit together, braid, interweave, construct, fabricate, build," from PIE root *teks- "to weave, to fabricate, to make; make wicker or wattle framework" (see texture (n.)).
An ancient metaphor: thought is a thread, and the raconteur is a spinner of yarns -- but the true storyteller, the poet, is a weaver. The scribes made this old and audible abstraction into a new and visible fact. After long practice, their work took on such an even, flexible texture that they called the written page a textus, which means cloth. [Robert Bringhurst, "The Elements of Typographic Style"]
Meaning "a digital text message" is from 2005.
text (v.): "to send a text message by mobile system," 2005; see text (n.). Related: Texted; texting. Formerly it meant "to write in text letters" (1590s), text letters being a kind of large writing used by clerks in the text or body of a manuscript (distinguished from the smaller hand used in the notes).