crisp: [OE] Historically, crisp means ‘curly’. It was borrowed into Old English from Latin crispus ‘curled’ (which was also the source of French crêpe, acquired by English as crape in the 17th century and then reborrowed in the original French form in the 19th century). The reason for the emergence of the word’s modern sense ‘brittle’, which happened in the early 16th century, is not clear, it may simply be that the sound of the word suggested brittleness. => crape, crêpe
crisp (adj.)
Old English crisp "curly," from Latin crispus "curled, wrinkled, having curly hair," from PIE root *(s)ker- (3) "to turn, bend" (see ring (n.)). It began to mean "brittle" 1520s, for obscure reasons, perhaps based on what happens to flat things when they are cooked. Figurative sense of "neat, brisk" is from 1814; perhaps a separate word. As a noun, from late 14c. Potato crisps (the British version of U.S. potato chips) is from 1929.
crisp (v.)
late 14c., "to curl," from crisp (adj.). Meaning "to become brittle" is from 1805. Related: Crisped; crisping.