proportion n.

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.

*perə-, Proto-Indo-European root meaning "to grant, allot" (and reciprocally, "to get in return"); possibly related to *pere- (1) "to produce, procure."

It forms all or part of: apart; apartment; bipartient; bipartisan; bipartite; compartment; depart; department; ex parte; impart; jeopardy; multipartite; parcel; parse; part; partial; participate; participation; particle; particular; particulate; partisan; partition; partitive; partner; party; portion; proportion; quadripartite; repartee; tripartite.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit purtam "reward;" Hittite parshiya- "fraction, part;" Greek peprotai "it has been granted;" Latin partem (nominative pars) "a part, piece," portio "share, portion."