"sikly envelop which the larvae of many insects spin as a covering while they are in the crysalis state," 1690s, from Middle French coucon (16c., Modern French cocon), from coque "clam shell, egg shell, nut shell," from Old French coque "shell," from Latin coccum "berry," from Greek kokkos "berry, seed" (see cocco-). The sense of "one's interior comfort place" is from 1986. Also see -oon.