"planned, put forth as a project," 1706, past-participle adjective from project (v.). In Middle English and early Modern English the adjective was simply project.

1690s, "caused by impulse;" 1715, "impelling, throwing;" see project (v.) + -ile. By 1865 as "capable of being thrust forward." Projectile vomiting is attested from 1985. 

late 15c., projeccioun, in alchemy, "transmutation by casting a powder on molten metal," from Old French projeccion and directly from Latin proiectionem (nominative proiectio) "a throwing forward, a stretching out," noun of action from past-participle stem of proicere "stretch out, throw forth" (see project (v.)).

From 1560s in the cartographical sense of "system of continuous correspondence between the points of a spherical surface and those of a plane." From 1590s as "action of projecting." From 1756 as "that which projects or juts out."

1590s, "one who forms a project or projects," agent noun in Latin form from project (v.). In the sense of "camera with a light source for throwing an image on a screen" it is attested from 1884.

Proto-Indo-European root forming prepositions, etc., meaning "forward," and, by extension, "in front of, before, first, chief, toward, near, against," etc.

It forms all or part of: afford; approach; appropriate; approve; approximate; barbican; before; deprive; expropriate; far; first; for; for-; fore; fore-; forefather; foremost; former (adj.); forth; frame; frau; fret; Freya; fro; froward; from; furnish; furniture; further; galore; hysteron-proteron; impervious; improbity; impromptu; improve; palfrey; par (prep.); para- (1) "alongside, beyond; altered; contrary; irregular, abnormal;" paradise; pardon; paramount; paramour; parvenu; pellucid; per; per-; percent; percussion; perennial; perestroika; perfect; perfidy; perform; perfume; perfunctory; perhaps; peri-; perish; perjury; permanent; permeate; permit; pernicious; perpendicular; perpetual; perplex; persecute; persevere; perspective; perspire; persuasion; pertain; peruse; pervade; pervert; pierce; portray; postprandial; prae-; Prakrit; pre-; premier; presbyter; Presbyterian; preterite; pride; priest; primal; primary; primate; primavera; prime; primeval; primitive; primo; primogenitor; primogeniture; primordial; primus; prince; principal; principle; prior; pristine; private; privilege; privy; pro (n.2) "a consideration or argument in favor;" pro-; probably; probe; probity; problem; proceed; proclaim; prodigal; produce; profane; profess; profile; profit; profound; profuse; project; promise; prompt; prone; proof; proper; property; propinquity; prophet; prose; prostate; prosthesis; protagonist; Protean; protect; protein; Proterozoic; protest; proto-; protocol; proton; protoplasm; Protozoa; proud; prove; proverb; provide; provoke; prow; prowess; proximate; Purana; purchase; purdah; reciprocal; rapprochement; reproach; reprove; veneer.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit pari "around, about, through," parah "farther, remote, ulterior," pura "formerly, before," pra- "before, forward, forth;" Avestan pairi- "around," paro "before;" Hittite para "outside of," Greek peri "around, about, near, beyond," pera "across, beyond," paros "before," para "from beside, beyond," pro "before;" Latin pro "before, for, on behalf of, instead of," porro "forward," prae "before," per "through;" Old Church Slavonic pra-dedu "great-grandfather;" Russian pere- "through;" Lithuanian per "through;" Old Irish ire "farther," roar "enough;" Gothic faura "before," Old English fore (prep.) "before, in front of," (adv.) "before, previously," fram "forward, from," feor "to a great distance, long ago;" German vor "before, in front of;" Old Irish air- Gothic fair-, German ver-, Old English fer-, intensive prefixes.

word-forming element meaning "forward, forth, toward the front" (as in proclaim, proceed); "beforehand, in advance" (prohibit, provide); "taking care of" (procure); "in place of, on behalf of" (proconsul, pronoun); from Latin pro (adv., prep.) "on behalf of, in place of, before, for, in exchange for, just as," which also was used as a first element in compounds and had a collateral form por-.

Also in some cases from cognate Greek pro "before, in front of, sooner," which also was used in Greek as a prefix (as in problem). Both the Latin and Greek words are from PIE *pro- (source also of Sanskrit pra- "before, forward, forth;" Gothic faura "before," Old English fore "before, for, on account of," fram "forward, from;" Old Irish roar "enough"), extended form of root *per- (1) "forward," hence "in front of, before, toward, near," etc.

The common modern sense of "in favor of, favoring" (pro-independence, pro-fluoridation, pro-Soviet, etc.) was not in classical Latin and is attested in English from early 19c.

*yē-, Proto-Indo-European root meaning "to throw, impel."

It forms all or part of: abject; abjection; adjacence; adjacent; adjective; aphetic; catheter; circumjacent; conjecture; deject; ease; ejaculate; eject; enema; gist; ictus; interjacent; inject; interject; interjection; jess; jet (v.1) "to sprout or spurt forth, shoot out;" jet (n.1) "stream of water;" jete; jetsam; jettison; jetton; jetty (n.) "pier;" joist; jut; object; objection; objective; paresis; project; projectile; reject; rejection; subjacent; subject; subjective; trajectory.

It is the hypothetical source of/evidence for its existence is provided by: Hittite ijami "I make;" Latin iacere "to throw, cast."