early 15c., contraccioun, "action of making a contract" (especially of marriage), a sense now obsolete; also "action of reducing, abridging, or shortening," from Old French contraction (13c.) or directly from Latin contractionem (nominative contractio) "a drawing together, an abridging, shortening, a shortening in pronunciation," noun of action from past-participle stem 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)). Related: Contractional.
Meaning "action of becoming shorter or smaller through the drawing together of the parts" is from 1580s. Meaning "action of acquiring (a disease) is from 1680s. Grammatical sense of "a shortening of a word or syllable in pronunciation or writing" is from 1706; meaning "a contracted word or words" is from 1755. Contractions of the uterus in labor of childbirth attested from 1962.