Quiz: Remember the definition of mal de mer?
messed up or disarrayed, esp. the hair; untidy
Old French descheveler 'to disarrange the hair'
also dishevelled, early 15c., "without dressed hair," parallel form of dishevel (adj.); see dishevel. General sense of "with disordered dress" is from c.1600.
originally an adjective, "bare-headed," late 14c., variant (with muted final -e) of dishevely, from Old French deschevele "bare-headed, with shaven head," past participle adjective from descheveler "to disarrange the hair," from des- "apart" (see dis-) + chevel "hair," from Latin capillus "hair" (see capillary). Of the hair, "dissheveled," mid-15c. OED says use as a verb is chiefly a back-formation from disheveled.