- any of various free-swimming, mostly marine cnidarians (esp. class Scyphozoa) with a body made up largely of jellylike substance and shaped like an umbrella: it has long, hanging tentacles with stinging cells on them
- Informal a weak-willed person
nounpl. jellyfish or jel·ly·fish·es
- a. Any of numerous usually free-swimming marine cnidarians of the class Scyphozoa, characteristically having a gelatinous, tentacled, often bell-shaped medusa stage as the dominant phase of its life cycle. Also called true jellyfish.b. Any of various similar or related cnidarians.
- Informal One who lacks force of character; a weakling.
(plural jellyfish or jellyfishes)
- (zoology) An almost transparent aquatic being; any one of the acalephs, especially one of the larger species, having a jellylike appearance.