also pro-rate, "divide or distribute proportionally, assess pro rata," 1860, American English, verb derived from Latin pro rata (parte); see pro rata. Related: Prorated; prorating.
1866 as a shortening of professional (n.). The adjective is attested by 1915 (in golfing's pro shop, workshop run by the resident professional at a club). The use of professional in reference to prostitutes seems to have accounted for proette in sports writing for "female pro golfer" (1968).
"a consideration or argument in favor," c. 1400, from Latin pro (prep.) "on behalf of, in place of, before, for, in exchange for, just as" (from PIE root *per- (1) "forward," hence "in front of, before, first, chief"). Pro and con is short for pro and contra (c. 1400) "for and against" (Latin pro et contra).
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.