"colleague, associate," 1510s, from collateral (adj.). Meaning "something of value given as security" is from 1832, American English, from phrase collateral security "property, etc., given to secure the performance of a contract" (1720), in which collateral (adj.) has the sense of "aiding or confirming in a secondary way."
late 13c., "to join in marriage" (transitive), from Old French alier "combine, unite," from a differentiated stem of aliier (from Latin alligare "bind to, tie to," from ad "to" (see ad-) + ligare "to bind, bind one thing to another, tie" (from PIE root *leig- "to tie, bind"). Meaning "to form an alliance, join, associate" is late 14c. Related: allied; allying.
member of an irregular monastic order of priests in the Middle Ages in the Celtic lands of the British Isles, mid-12c., from Old Irish céle de "anchorite," from cele "associate, companion," sometimes "servant" (compare ceilidh) + de "of God." Perhaps an attempt to translate Servus Dei or some other Latin term for "religious hermit." Related: Culdean.
"of or pertaining to sale, sales, or the business of selling," word-forming element from genitive of sale (n.), by 1520s, in salesman. Cf. saleswork "work done for sale" (1775). For earlier use of similar formations, compare craftsman, oarsman, both Middle English. Sales tax is attested by 1886; sales clerk by 1863; sales associate by 1946. Sales representative is from 1910.
also co-operate, "to act or operate jointly with another or others to the same end," c. 1600, from Late Latin cooperatus, past participle of cooperari "to work together with," from assimilated form of com "with, together" (see com-) + operari "to work," from PIE root *op- "to work, produce in abundance." Cooperator "fellow worker, associate" is attested from early 15c. Related: Cooperated; cooperating.
"an associate in office, employment, or labor," 1530s, from French collègue (16c.), from Latin collega "partner in office," from assimilated form of com "with, together" (see com-) + leg-, stem of legare "send as a deputy, send with a commission," from PIE root *leg- (1) "to collect, gather." So, "one sent or chosen to work with another," or "one chosen at the same time as another."
"companion" (obsolete), from Middle English fere, a shortening of Old English gefera "associate, comrade, fellow-disciple; wife, man, servant," from Proto-Germanic *forjanan, from the causative of *faranan (source of Old English faran "to go, travel"), from PIE root *per- (2) "to lead, pass over." Literally "one who goes with another." Compare German Gefährte "companion," from the same root; also, from causative *forjan-, Old High German fuoren. "to lead," modern German Fuhrer.