mid-14c., "smash, shatter, break into fragments or small particles; force down and bruise by heavy weight," also figuratively, "overpower, subdue," from Old French cruissir (Modern French écraser), variant of croissir "to gnash (teeth), crash, smash, break," which is perhaps from Frankish *krostjan "to gnash" (cognates: Gothic kriustan, Old Swedish krysta "to gnash").
Figurative sense of "to humiliate, demoralize" is by c. 1600. Related: Crushed; crushing; crusher. Italian crosciare, Catalan cruxir, Spanish crujirare "to crack" are Germanic loan-words.
1590s, "act of crushing, a violent collision or rushing together," from crush (v.). Meaning "thick crowd" is from 1806. Sense of "person one is infatuated with" is first recorded 1884, U.S. slang; to have a crush on (someone) is by 1903.