Is it ensure, insure, or assure?
mid-14c., from Old French cruissir (Modern French écraser), variant of croissir "to gnash (teeth), crash, break," perhaps from Frankish *krostjan "to gnash" (cf. Gothic kriustan, Old Swedish krysta "to gnash"). Figurative sense of "to humiliate, demoralize" is c.1600. Related: Crushed; crushing. Italian crosciare, Catalan cruxir, Spanish crujirare "to crack" are Germanic loan-words.
1590s, "act of crushing," from crush (v.). Meaning "thick crowd" is from 1806. Sense of "person one is infatuated with" is first recorded 1884; to have a crush on is from 1913.