contractual (adj.)

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.