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.

c. 1300, pur blind "entirely blind," as a noun, "a blind person," later "partially blind, blind in one eye" (late 14c.), the main modern sense, from blind (adj.) + pur "entirely, completely, absolutely."

The adverb forming the first element is from an identical Middle English adjective pur "unadulterated, unmixed" (c. 1300), usually explained as from Old French pur and Latin purus (see pure). It might have been influenced by the Anglo-French perfective prefix pur- (see pur-). The sense of "dull" is recorded from 1530s.

c. 1300, purchasen, "acquire, obtain; get, receive; procure, provide," also "accomplish or bring about; instigate; cause, contrive, plot; recruit, hire," from Anglo-French purchaser "go after," Old French porchacier "search for, procure; purchase; aim at, strive for, pursue eagerly" (11c., Modern French pourchasser), from pur- "forth" (possibly used here as an intensive prefix; see pur-) + Old French chacier "to run after, hunt, chase" (see chase (v.)).

Originally to obtain or receive as due in any way, including through merit or suffering; the specific sense of "acquire or secure by expenditure of money or its equivalent, pay money for, buy" is attested from mid-14c., though the word continued to be used for "to get by conquest in war, obtain as booty" up to 17c. Related: Purchased; purchasing.

early 15c., "meaning, tenor, the surface or expressed meaning of a document, etc.; that which is conveyed or expressed," from Anglo-French purport (late 13c.), Old French porport "contents, tenor," back-formation from purporter "to contain, convey, carry; intend," from pur- (from Latin pro- "forth;" see pur-) + Old French porter "to carry," from Latin portare "to carry" (from PIE root *per- (2) "to lead, pass over"). Meaning "that which is to be done or effected" is from 1650s.

1520s, "indicate, express, set forth, convey to the mind as the meaning or thing intended," from the noun in English and from Anglo-French purporter (c. 1300), from Old French purporter "to contain, convey, carry; intend," from pur- (from Latin pro- "forth;" see pur-) + Old French porter "to carry," from Latin portare "to carry" (from PIE root *per- (2) "to lead, pass over"). Related: Purported; purporting.

c. 1300, purpus, "intention, aim, goal; object to be kept in view; proper function for which something exists," from Anglo-French purpos, Old French porpos "an aim, intention" (12c.), from porposer "to put forth," from por- "forth" (from a variant of Latin pro- "forth;" see pur-) + Old French poser "to put, place" (see pose (v.1)).

Etymologically it is equivalent to Latin propositium "a thing proposed or intended," but evidently formed in French from the same elements. From mid-14c. as "theme of a discourse, subject matter of a narrative (as opposed to digressions), hence to the purpose "appropriate" (late 14c.). On purpose "by design, intentionally" is attested from 1580s; earlier of purpose (early 15c.).