"act of shaking, concussion," early 15c., quassacioun, from Latin quassationem (nominative quassatio) "a shaking or beating," noun of action from past-participle stem of quassare "to shatter, shake or toss violently" (see quash).
"water-tight, barrel-like vessel for containing liquids," mid-15c., from French casque "a cask; a helmet," from Spanish casco "skull; wine-vat; helmet," originally "potsherd," from cascar "to break up," from Vulgar Latin *quassicare, frequentative of Latin quassare "to shake, shatter" (see quash). The sense evolution is uncertain.
late 14c., crasen, craisen "to shatter, crush, break to pieces," probably a Germanic word and perhaps ultimately from a Scandinavian source (such as Old Norse *krasa"shatter"), but it seems to have entered English via Old French crasir (compare Modern French écraser). Original sense preserved in crazy quilt (1886) pattern and in reference to cracking in pottery glazing (1815).
Mental sense of "derange the intellect of, make insane" (late 15c.) perhaps comes via the transferred sense of "be diseased or deformed" (mid-15c.), or it might be an image of cracked or broken things. The intransitive sense of "become insane" is by 1818. Related: Crazed; crazing.
... there is little assurance in reconciled enemies: whose affections (for the most part) are like unto Glasse; which being once cracked, can neuer be made otherwise then crazed and vnsound. [John Hayward, "The Life and Raigne of King Henrie the IIII," 1599]