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.
c. 1500, "thing that mashes," agent noun from mash (v.). Meaning "would-be lady-killer, one whose dress or manners are such as to impress strongly the fancy of susceptible young women" is by 1875, American English, perhaps in use from 1860, probably from mash (v.) on notion either of "pressing one's attentions" or "crushing someone else's emotions" (compare crush (n.)).
He was, to use a Western expression, a 'regular heart-smasher among the women;' and it may not be improper to state, just here, that no one had a more exalted opinion of his capabilities in that line than the aforesaid 'Jo' himself. [Harper's New Monthly Magazine, March 1861]
He had a weakness to be considered a regular masher of female hearts and a very wicked young man with the fair sex generally, but there was not a well-authenticated instance of his ever having broken a heart in his life, nor likely to be one. [Gilbert A. Pierce, "Zachariah, The Congressman," Chicago, 1880]
Also in use in late 19c were mash (n.) "a romantic fixation, a crush" (1882); mash (v.) "excite sentimental admiration" (1882); mash-note "love letter" (1890).
outermost of the three bones inside the human ear, 1660s, from Latin malleus "a hammer" (from PIE root *mele- "to crush, grind"). So called for its shape.