cocoon
co.coon \k*-'ku:n\ n [F cocon, fr. Prov coucoun, fr. coco shell, fr. L coccumX excrescence on a tree, fr. Gk kokkos grain seed, kermes berry 1a: an envelope often largely of silk which an insect larva forms about its elf and in which it passes the pupa stage 1b: any of various other protective coverings produced by animals 2: a covering suggesting a cocoon; specif : a protective covering p laced or sprayed over military or naval equipment in storage