ˈ ̷ ̷ ̷ ̷ˌ ̷ ̷ noun
1.
a. : any of various usually marine and free-swimming coelenterates that constitute the sexually reproducing form of hydrozoans and scyphozoans which exhibit alternation of a sexual and an asexual generation and that have a nearly transparent saucer-shaped body with a mouth on the underside which extends by radially situated gastrovascular canals to the margin of the body, extensile marginal tentacles studded with stinging cells, and various sense organs distributed along the margin of the body — called also sea nettle
b. : siphonophore
c. : ctenophore — not used technically
2. : a person lacking backbone or firmness
if I should yield to threats … I should be a jellyfish by this time — Elinore M. Herrick