Online Etymology Dictionary

peninsula (n.): 1530s, from Latin pæninsula "a peninsula," literally "almost an island," from pæne "almost" + insula "island" (see isle). Earlier translated as demie island.
peninsular (adj.): 1610s, from peninsula + -ar.
penis (n.): 1670s, perhaps from French pénis or directly from Latin penis "penis," earlier "tail," from PIE *pes- "penis" (source also of Sanskrit pasas-, Greek peos, posthe "penis," probably also Old English fæsl "progeny, offspring," Old Norse fösull, German Fasel "young of animals, brood"). The proper plural is penes. The adjective is penial. In psychological writing, penis envy is attested from 1924.
penitence (n.): c. 1200, from Old French penitence (11c.) and directly from Latin paenitentia "repentance," noun of condition from paenitentum (nominative paenitens) "penitent," present participle of paenitere "cause or feel regret," probably originally "is not enough, is unsatisfactory," from paene "nearby, almost."
penitent (adj.): mid-14c., from Old French pénitent (14c.) and directly from Latin paenitentem (see penitence). As a noun, late 14c., from the adjective.
penitential (adj.): c. 1500, from Medieval Latin penitentialis, from Latin paenitentia "repentance" (see penitence).
penitentiary (n.): early 15c., "place of punishment for offenses against the church," from Medieval Latin penitentiaria, from fem. of penitentiarius (adj.) "of penance," from Latin paenitentia "penitence" (see penitence). Meaning "house of correction" (originally an asylum for prostitutes) is from 1806, short for penitentiary house (1776). Slang shortening pen is attested from 1884.
penknife (n.): early 15c., from pen (n.1) + knife (n.). So called because such small knives were used to sharpen quills.
penman (n.): 1610s, "copyist, clerk, scrivener" (obsolete), from pen (n.1) + man (n.).
penmanship (n.): 1690s, from obsolete penman "copyist, clerk, scrivener" + -ship.
pennant (n.): 1610s, "rope for hoisting," probably a blend of pendant in the nautical sense of "suspended rope" and pennon. Use for "flag on a warship" first recorded 1690s; "flag symbolizing a sports championship" (especially baseball) is from 1880; as a synonym for "championship" it was first used 1915.
penniless (adj.): "destitute," early 14c., penyles, from penny + -less.
pennon (n.): long, narrow flag (often triangular or swallow-tailed), late 14c., from Old French penon "feathers of an arrow; streamer, flag, banner," from penne "feather," from Latin penna "feather" (see pen (n.1)).
Pennsylvania: American colony, later U.S. state, 1681, literally "Penn's Woods," a hybrid formed from the surname Penn (Welsh, literally "head") + Latin sylvania (see sylvan). Not named for William Penn, the proprietor, but, on suggestion of Charles II, for Penn's late father, Admiral William Penn (1621-1670), who had lent the king the money that was repaid to the son in the form of land for a Quaker settlement in America. The story goes that the younger Penn wanted to call it New Wales, but the king's secretary, a Welshman of orthodox religion, wouldn't hear of it. Pennsylvania Dutch is attested from 1824.
Pennsylvanian (adj.): 1698, from Pennsylvania + -an. In reference to a geological system, attested from 1891. As a noun meaning "a person of Pennsylvania," by 1685.
penny (n.): Old English pening, penig, Northumbrian penning "penny," from Proto-Germanic *panninggaz (source also of Old Norse penningr, Swedish pänning, Danish penge, Old Frisian panning, Old Saxon pending, Middle Dutch pennic, Dutch penning, Old High German pfenning, German Pfennig, not recorded in Gothic, where skatts is used instead), of unknown origin.
Offa's reformed coinage on light, broad flans is likely to have begun c.760-5 in London, with an awareness of developments in Francia and East Anglia. ... The broad flan penny established by Offa remained the principal denomination, with only minor changes, until the fourteenth century. [Anna Gannon, "The Iconography of Early Anglo-Saxon Coinage," Oxford, 2003]
The English coin was originally set at one-twelfth of a shilling and was of silver, later copper, then bronze. There are two plural forms: pennies of individual coins, pence collectively. In translations it rendered various foreign coins of small denomination, especially Latin denarius, whence comes its abbreviation d.

As American English colloquial for cent, it is recorded from 1889. Penny-a-liner "writer for a journal or newspaper" is attested from 1834. Penny dreadful "cheap and gory fiction" dates from c. 1870. Phrase penny-wise and pound-foolish is recorded from c. 1600. Penny-pincher "miserly person" is recorded from 1906 (as an adjective penny-pinching is recorded from 1858, American English). Penny loafers attested from 1960.
penny-ante (adj.): "cheap, trivial," 1935; extended from use in reference to poker played for insignificant stakes (1855), from penny + ante.
pennyfarthing (adj.): also penny farthing, penny-farthing, "ineffective," 1887, from penny + farthing, the two together making but a small sum. The noun, in reference to the kind of bicycle with a small wheel in back and a big one in front (so called from the notion of different size coins) is first recorded 1927.
pennyroyal (n.): herb, 1520s, alteration by folk etymology of Anglo-French puliol real; for second element see royal; first element ultimately from Latin puleium "thyme," of unknown origin.
pennyweight (n.): Old English penega gewiht, originally the weight of a silver penny; see penny + weight (n.).
pennyworth (n.): Old English peningwurð; see penny + worth (adj.). Figurative of "small amount" from mid-14c.
penology (n.): "study of punishment and crime prevention," 1838, coined apparently by Francis Lieber, corresponding member of the Philadephia Society for Alleviating the Miseries of Public Prisons, from pen- as in penitentiary (ultimately from Latin poena "penalty, punishment;" see penal) + -ology "study of." Related: Penologist; penological.
Pensacola: name of a Muskogean tribe, from Choctaw, literally "hair-people," from pashi "hair of the head" + oklah "people."
pension (n.): mid-14c., "payment for services," especially "reward, payment out of a benefice" (early 14c., in Anglo-Latin), from Old French pension "payment, rent" (13c.) and directly from Latin pensionem (nominative pensio) "a payment, installment, rent," from past participle stem of pendere "pay, weigh" (see pendant). Meaning "regular payment in consideration of past service" first recorded 1520s. Meaning "boarding house, boarding school" first attested 1640s, from French, and usually in reference to places in France or elsewhere on the Continent.
pension (v.): 1640s, "to live in a pension," from pension (n.) or else from French pensionner. Meaning "to grant a pension" is from 1702. Related: Pensioned; pensioning.
pensioner (n.): late 15c., from Anglo-French pensionner, from Old French pensionnier (mid-14c.), from Medieval Latin pensionarius, from pension (see pension (n.)).
pensive (adj.): late 14c., from Old French pensif "thoughtful, distracted, musing" (11c.), from penser "to think," from Latin pensare "weigh, consider," frequentative of pendere "weigh" (see pendant). Related: Pensively; pensiveness.
pent (adj.): "kept in, confined," 1540s, variant of penned, past participle of pen (v.2). Pent-up (also pent up) is from 1580s.
penta-: word-forming element meaning "five, containing five," from Greek penta- (before a vowel pent-), comb. form of pente "five," related to Aeolian pempte (see five), with -a- by analogy of hepta-, ennea-, deka-.
pentacle (n.): 1590s, from Medieval Latin pentaculum "pentagram," a hybrid coined from Greek pente "five" (see five) + Latin -culum, diminutive (or instrumental) suffix. OED notes other similar words: Italian had pentacolo "anything with five points," and French pentacle (16c.) was the name of something used in necromancy, perhaps a five-branched candlestick; French had pentacol "amulet worn around the neck" (14c.), from pend- "to hang" + a "to" + col "neck." The same figure as a pentagram, except in magical usage, where it has been extended to other symbols of power, including a six-point star. Related: Pentacular.
pentad (n.): 1650s, from Greek pentas (genitive pentados) "group of five" (see five). Meaning "period of five years" is from 1880; meaning "period of five days" is from 1906, originally in meteorology.
pentagon (n.): plane figure with five angles and five sides, 1560s, from Middle French pentagone or directly from Late Latin pentagonum "pentagon," from Greek pentagonon, noun use of neuter of adjective pentagonos "five-angled," from pente "five" (see five) + gonia "angle" (see -gon). The U.S. military headquarters Pentagon was completed 1942, so called for its shape; used allusively for "U.S. military leadership" from 1945. Related: Pentagonal.
In nature, pentagonal symmetry is rare in inanimate forms. Packed soap bubbles seem to strive for it but never quite succeed, and there are no mineral crystals with true pentagonal structures. But pentagonal geometry is basic to many living things, from roses and forget-me-nots to sea urchins and starfish. [Robert Bringhurst, "The Elements of Typographic Style," 1992]
pentagram (n.): "five-pointed star," 1820, from Greek pentagrammon, noun use of neuter of adj. pentagrammos "having five lines," from pente "five" (see five) + gramma "letter, character, what is written" (see -gram).
pentameter (adj.): 1540s, from Middle French pentametre, from Latin pentameter, from Greek pentametros (adj.) "having five measures," from pente "five" (see five) + metron "measure" (see meter (n.2)). As a noun from 1580s.
pentangle (n.): c. 1300; see penta- + angle (n.). In some early uses perhaps a corruption of pentacle. Related: Pentangular.
Pentateuch: first five books of the Bible, c. 1400, from Late Latin pentateuchus (Tertullian, c.207), from Greek pentateukhos (c. 160), originally an adjective (abstracted from phrase pentateukhos biblos), from pente "five" (see five) + teukhos "implement, vessel, gear" (in Late Greek "book," via notion of "case for scrolls"), literally "anything produced," related to teukhein "to make ready," from PIE *dheugh- "to produce something of utility" (see doughty). Glossed in Old English as fifbec.
pentathlon (n.): athletic contest of five events, 1852, from Greek pentathlon "the contest of five exercises," from pente "five" (see five) + athlon "prize, contest," of uncertain origin. Earlier in English in Latin form pentathlum (1706). The Greek version consisted of jumping, sprinting, discus and spear throwing, and wrestling. The modern version (1912) consists of horseback riding, fencing, shooting, swimming, and cross-country running.
Pentecost: Old English Pentecosten "Christian festival on seventh Sunday after Easter," from Late Latin pentecoste, from Greek pentekoste (hemera) "fiftieth (day)," fem. of pentekostos, from pentekonta "fifty," from pente "five" (see five). The Hellenic name for the Old Testament Feast of Weeks, a Jewish harvest festival observed on 50th day of the Omer (see Lev. xxiii:16).
pentecostal: 1660s, "pertaining to the Pentecost," from Latin pentecostalis (Tertullian), from pentecoste (see pentecost). With a capital P- and meaning "Pentecostalist," in reference to "Christian sect emphasizing gifts of the Holy Spirit" (Acts ii), it is attested from 1904 (noun and adjective).
penthouse (n.): pendize, early 14c., from Anglo-French pentiz, a shortening of Old French apentis "attached building, appendage," from Medieval Latin appendicium, from Latin appendere "to hang" (see append). Modern spelling is from c. 1530, by folk etymology influence of Middle French pente "slope," and English house (the meaning at that time was "attached building with a sloping roof or awning"). Originally a simple structure (Middle English homilies describe Jesus' birthplace in the manger as a "penthouse"); meaning "apartment or small house built on the roof of a skyscraper" first recorded 1921, from which time dates its association with luxury.
Pentothal: trademark name of an anaesthetic and hypnotic, 1935, refashioning of Thiopental, from pento-, in reference to the methylbutyl five-carbon group + first two letters of thiobarbiturate + chemical product suffix -ol.
penult (adj.): "last but one," 1530s, abbreviation of penultima. As a noun from 1570s.
penultima (n.): 1580s, from Latin penultima (syllaba), "the next to the last syllable of a word or verse," from fem. of Latin adjective penultimus "next-to-last," from paene "almost" + ultimus "final" (see ultimate).
penultimate (adj.): 1670s, from penultima (n.) on model of proximate.
penumbra (n.): 1660s, from Modern Latin penumbra "partial shadow outside the complete shadow of an eclipse," coined 1604 by Kepler from Latin pæne "almost" + umbra "shadow" (see umbrage). Related: Penumbral.
penurious (adj.): 1590s, from penury + -ous, or else from Medieval Latin penuriosus, from Latin penuria "penury." Originally "poverty-stricken, in a state of penury;" meaning "stingy" is first attested 1630s. Related: Penuriously.
penury (n.): c. 1400, from Latin penuria "want, need; scarcity," related to paene "scarcely."
Penzance: place in Cornwall, Pensans (late 13c.), literally "Holy Headland," from Cornish penn "head" + sans "holy."
peon (n.): unskilled worker, 1826, from Mexican Spanish peon "agricultural laborer" (especially a debtor held in servitude by his creditor), from Spanish peon "day laborer," also "pedestrian," originally "foot soldier," from Medieval Latin pedonem "foot soldier" (see pawn (n.2)). The word entered British English earlier (c. 1600) in the sense "native constable, soldier, or messenger in India," via Portuguese peao "pedestrian, foot soldier, day laborer."
peonage (n.): 1848, American English, from peon + -age.