subcontract n.

word-forming element meaning "under, beneath; behind; from under; resulting from further division," from Latin preposition sub "under, below, beneath, at the foot of," also "close to, up to, towards;" of time, "within, during;" figuratively "subject to, in the power of;" also "a little, somewhat" (as in sub-horridus "somewhat rough"), from PIE *(s)up- (perhaps representing *ex-upo-), a variant form of the root *upo "under," also "up from under." The Latin word also was used as a prefix and in various combinations.

In Latin assimilated to following -c-, -f-, -g-, -p-, and often -r- and -m-. In Old French the prefix appears in the full Latin form only "in learned adoptions of old Latin compounds" [OED], and in popular use it was represented by sous-, sou-; as in French souvenir from Latin subvenire, souscrire (Old French souzescrire) from subscribere, etc.

The original meaning is now obscured in many words from Latin (suggest, suspect, subject, etc.). The prefix is active in Modern English, sometimes meaning "subordinate" (as in subcontractor); "inferior" (17c., as in subhuman); "smaller" (18c.); "a part or division of" (c. 1800, as in subcontinent).

early 14c., "agreement between two or more persons to do or not do some particular thing," originally especially of marriage, from Old French contract (Modern French contrat), from Latin contractus "a drawing together, a shrinking; a contract, an agreement," from past participle of contrahere "to draw several objects together; draw in, shorten, lessen, abridge," metaphorically "make a bargain, make an agreement," from assimilated form of com "with, together" (see con-) + trahere "to draw" (see tract (n.1)).

In reference to the writing which contains the agreement and its terms and conditions, 1610s. U.S. underworld sense of "arrangement to kill someone" first recorded 1940.

1810, from sub- + contractor, or else an agent noun from subcontract.