Online Etymology Dictionary

prostatitis (n.): 1844, from prostate + -itis "inflammation."
prosthesis (n.): 1550s, "addition of a letter or syllable to a word," from Late Latin, from Greek prosthesis "addition," from prostithenai "add to," from pros "to" + tithenai "to put, place" (see theme). Meaning "artificial body part" is first recorded c. 1900, from earlier use to describe the medical art of making artificial limbs (1706), on notion of "that which is added to" the injured body.
prosthetic (adj.): 1837 in grammar; 1902 in the surgical sense, from Latinized form of Greek prosthetikos "disposed to add," from prosthetas "added," verbal adjective of prostithenai "to put to, add to" (see prosthesis). Related: Prosthetically.
prosthetics (n.): 1894, from prosthetic; also see -ics.
prostitute (v.): 1520s, "to offer to indiscriminate sexual intercourse (usually in exchange for money)," from Latin prostitutus, past participle of prostituere "to expose to prostitution, expose publicly," from pro- "before" (see pro-) + statuere "cause to stand, establish," from PIE root *stā- "to stand," with derivatives meaning "place or thing that is standing" (see stet). Related: Prostituted; prostituting.

The notion of "sex for hire" is not inherent in the etymology, which rather suggests one "exposed to lust" or sex "indiscriminately offered." However, this is now almost the official European term for the institution: German prostituierte, Russian prostitutka, etc. Figurative sense (of abilities, etc.) is from 1570s. Of men, in reference to homosexual acts, from 1886 (in form prostitution); phrase male prostitute attested by 1948.
prostitute (n.): "harlot, woman who offers her body indiscriminately" (usually for money)," 1610s, from Latin prostituta "prostitute," fem. of prostitutus, past participle of prostituere (see prostitute (v.)).
prostitution (n.): 1530s, from Middle French prostitution and directly from Late Latin prostitutionem (nominative prostitutio), noun of action from past participle stem of prostituere (see prostitute).
prostomium (n.): 1870, Latinized form of Greek prostomion "fore-mouth, something before the mouth," from pro "before" (see pro-) + stoma "mouth" (see stoma).
prostrate (adj.): mid-14c., "lying face-down" (in submission, worship, etc.), from Latin prostratus, past participle of prosternere "strew in front, throw down," from pro- "forth" (see pro-) + sternere "to spread out," from PIE root *stere- "to spread, extend, stretch out" (see structure (n.)). Figurative use from 1590s. General sense of "laid out, knocked flat" is from 1670s.
prostrate (v.): early 15c., prostraten, "prostrate oneself," from prostrate (adj.). Related: Prostrated; prostrating.
prostration (n.): c. 1400, "action of prostrating oneself," from Old French prostracion (14c.) or directly from Late Latin prostrationem (nominative prostratio), noun of action from past participle stem of prosternere (see prostrate (v.)); or else a native formation from prostrate (v.). Meaning "weakness, exhaustion, dejection" is from 1650s.
prosy (adj.): 1814 (Jane Austen), from prose + -y (2). Related: Prosiness.
Prot (n.): colloquial shortening of Protestant (n.), used by Catholics, often contemptuous.
protagonist (n.): 1670s, "principal character in a story, drama, etc.," from Greek protagonistes "actor who plays the chief or first part," from protos "first" (see proto-) + agonistes "actor, competitor," from agon "contest" (see act (n.)). Meaning "leading person in any cause or contest" is from 1889. Mistaken sense of "advocate, supporter" (1935) is from misreading of Greek protos as Latin pro- "for."
Protean (adj.): 1590s, from Greek Proteus, sea god (son of Oceanus and Tethys) who could change his form; his name is literally "first," from protos "first" (see proto-).
protease (n.): 1903, from protein + -ase. Related: Proteolysis.
protect (v.): mid-15c., from Latin protectus, past participle of protegere "to protect, cover in front" (see protection). International economics sense from 1789. Related: Protected; protecting.
protectant (adj.): 1660s, irregularly formed from protect + -ant. As a noun from 1935.
protection (n.): mid-14c., "shelter, defense; keeping, guardianship;" late 14c. as "that which protects," from Old French proteccion "protection, shield" (12c.) and directly from Late Latin protectionem (nominative protectio) "a covering over," noun of action from past participle stem of protegere "protect, cover in front," from pro- "in front" + tegere "to cover" (see stegosaurus).

A common Old English word for "protect" was beorgan. International economic sense is from 1789. In gangster sense, "freedom from molestation in exchange for money," it is attested from 1860. Ecological sense of "attempted preservation by laws" is from 1880 (originally of wild birds in Britain). Also in medieval England, "the protection or maintenance of a lord or patron; sponsorship." To put (someone) out of protection meant to deprive him or her of the security of the protection of the kingdom's laws.
protectionism (n.): 1846, from protectionist + -ism.
protectionist (n.): in the economics sense, 1841, from French protectionniste (in political economy sense, protection is attested from 1789). As an adjective by 1843.
protective (adj.): 1660s, from protect + -ive. As a noun from 1875. Related: Protectively; protectiveness. Protective custody is from 1933, translating German Schutzhaft, used cynically by the Nazis.
protector (n.): late 14c., from Old French protector (14c., Modern French protecteur) and directly from Late Latin protector, agent noun from protegere (see protection). Related: Protectoral.
protectorate (n.): 1690s in reference to the government by the Cromwells; 1795 as "occupied territory of another nation," from protector + -ate (1). Meaning "state or territory (usually tribal) placed under the protection of a major power" is from 1860.
protege (n.): 1778, from French protégé (fem. protégée) "one who is protected," noun use of past participle of Middle French protéger "protect," from Latin protegere (see protect; also see protection).
protein (n.): 1844, from French protéine, coined 1838 by Dutch chemist Gerhard Johan Mulder (1802-1880), perhaps on suggestion of Berzelius, from Greek proteios "the first quality," from protos "first" (see proto-) + -ine (2).

Originally a theoretical substance thought to be essential to life, further studies of the substances he was working with overthrew this, but the words protein and proteid continued to be used in international work on the matter and also for other organic compounds; the modern use as a general name for a class of bodies arose in German. The confusion became so great a committee was set up in 1907 to sort out the nomenclature, which it did, giving protein its modern meaning and banishing proteid.
proteinuria: 1911, Modern Latin, from French protéinurie; see protein + urine + abstract noun ending -ia.
protero-: before vowels proter-, word-forming element meaning "former, earlier," from comb. form of Greek proteros "before, former, anterior," from PIE *pro-, from root *per- (1) "forward, through" (see per).
Proterozoic (adj.): 1880, from protero- + zoic.
protest (n.): c. 1400, "avowal, pledge, solemn declaration," from Old French protest (Modern French prôtet), from preotester, and directly from Latin protestari "declare publicly, testify, protest," from pro- "forth, before" (see pro-) + testari "testify," from testis "witness" (see testament).

Meaning "statement of disapproval" first recorded 1751; adjectival sense of "expressing of dissent from, or rejection of, prevailing mores" is from 1953, in reference to U.S. civil rights movement. First record of protest march is from 1959.
protest (v.): mid-15c., "to declare or state formally or solemnly," from Old French protester, from Latin protestari "declare publicly, testify, protest" (see protest (n.)). Original sense preserved in to protest one's innocence. Related: Protested; protesting.
Protestant (n., adj.): 1539, from German or French protestant, from Latin protestantem (nominative protestans), present participle of protestari (see protest (n.)). Originally used of German princes and free cities who declared their dissent from ("protested") the decision of the Diet of Speyer (1529), which reversed the liberal terms allowed Lutherans in 1526.
When forced to make their choice between obedience to God and obedience to the Emperor, they were compelled to choose the former. [Thomas M. Lindsay, "A History of the Reformation," New York, 1910]
The word was taken up by the Lutherans in Germany (Swiss and French preferred Reformed). It became the general word for "adherents of the Reformation in Germany," then "member of any Western church outside the Roman communion;" a sense first attested in English in 1553.
In the 17c., 'protestant' was primarily opposed to 'papist,' and thus accepted by English Churchmen generally; in more recent times, being generally opposed to 'Roman Catholic,' or ... to 'Catholic,' ... it is viewed with disfavour by those who lay stress on the claim of the Anglican Church to be equally Catholic with the Roman. [OED]
Often contemptuous shortened form Prot is from 1725, in Irish English. Protestant (work) ethic (1926) is taken from Max Weber's work "Die protestantische Ethik und der 'Geist' des Kapitalismus" (1904). Protestant Reformation attested by 1680s.
Protestantism (n.): 1640s, from French protestantisme or else formed from Protestant + -ism.
protestation (n.): mid-14c., "affirmation;" late 14c., "avowal, declaration, assertion," from Old French protestacion "protest, protestation" (13c.) and directly from Latin protestationem (nominative protestatio) "a declaration, protestation," noun of action from past participle stem of protestari (see protest (n.)).
protester (n.): also protestor, 1540s, "one who makes solemn affirmation;" agent noun from protest (v.). From 1960 as "demonstrator, public opponent of the established order."
Proteus: c. 1400, from Greek Proteus (see Protean).
prothalamion (n.): "song sung before a wedding," 1590s, coined as a poem title by Edmund Spenser (based on epithalamion) from Greek pro- "before" (see pro-) + thalamos "bridal chamber" (see thalamus). Sometimes Latinized as prothalamium.
prothesis (n.): from Greek prothesis "a placing before, a placing in public," from pro (see pro-) + thesis (see thesis). In ecclesiastical sense from 1670s; grammatical from 1870. Related: Prothetic (1835 in grammar); prothetical; prothetically.
prothonotary (n.): also protonotary, mid-15c., "principal clerk of a court," from Late Latin prothonotarius, from Greek protonotarios "first scribe," originally the recorder of the court of the Byzantine empire, from protos "first" (see proto-) + Latin notarius (see notary). The -h- appeared in Medieval Latin
protist (n.): 1869, from Modern Latin Protista (German Protisten, Haeckel, 1868), from Greek neuter plural of protistos "the very first," superlative of protos "first" (see proto-).
proto-: before vowels prot-, word-forming element meaning "first, source, parent, preceding, earliest form, original, basic," from Greek proto-, from protos "first," from PIE *pre-, from root *per- (1) "forward, through" (see per).
proto-language (n.): 1948, from proto- + language.
protocol (n.): 1540s, as prothogall "draft of a document," from Middle French prothocole (c. 1200, Modern French protocole), from Medieval Latin protocollum "draft," literally "the first sheet of a volume" (on which contents and errata were written), from Greek protokollon "first sheet glued onto a manuscript," from protos "first" (see proto-) + kolla "glue."

Sense developed in Medieval Latin and French from "official account" to "official record of a transaction," to "diplomatic document," and finally, in French, to "formula of diplomatic etiquette." Meaning "diplomatic rules of etiquette" in English first recorded 1896, from French; general sense of "conventional proper conduct" is from 1952. "Protocols of the (Learned) Elders of Zion," Russian anti-Semitic forgery purporting to reveal Jewish plan for world domination, first published in English 1920 under title "The Jewish Peril."
proton (n.): 1920 in physics, coined by English physicist Ernest Rutherford (1871-1937) from noun use of Greek proton, neuter of protos "first" (see proto-), on analogy of electron; supposedly because hydrogen was hypothesized as a constituent of all the elements. The word was used earlier in embryology (1893) as a translation of German anlage ("fundamental thing") based on Aristotle's phrase he prote ousia to proton.
protoplanet (n.): 1949, from proto- + planet.
protoplasm (n.): 1848, from German Protoplasma (1846), used by German botanist Hugo von Mohl (1805-1872), on notion of "first-formed," from Greek proto- "first" (see proto-) + plasma "something molded" (see -plasm).

The word was in Late Latin with a sense of "first created thing," and it might have existed in ecclesiastical Greek in a different sense. It was used 1839 by Czech physiologist Johannes Evangelista Purkinje (1787-1869) to denote the gelatinous fluid found in living tissue. The modern meaning is a refinement of this. This word prevailed, though German language purists preferred Urschleim.
protostar (n.): 1954, from proto- + star (n.).
prototype (n.): c. 1600, from French prototype (16c.) and directly from Medieval Latin prototypus "original, primitive," from Greek prototypon "a first or primitive form," noun use of neuter singular of prototypos "original, primitive," from protos "first" (see proto-) + typos "impression, mold, pattern" (see type (n.)). In English from 1590s as prototypon.
prototypical (adj.): 1640s, from prototype + -ical.
Protozoa (n.): 1828, from Modern Latin Protozoa, coined 1818 by German zoologist Georg August Goldfuss (1782-1848) from Greek protos "first" (see proto-) + zoia, plural of zoion "animal" (see zoo). Originally including sponges and corals; current sense is from 1845. Related: Protozoon (aingular); Protozoan.