box jellyfish
noun
variants:
or less commonly box jelly
Definition of box jellyfish
: any of various cube-shaped scyphozoan jellyfishes (order or suborder Cubomedusae) of tropical and warm marine waters that inflict a painful and sometimes fatal sting
especially
: an extremely venomous box jellyfish (Chironex fleckeri) of Australia that has a bell that may reach over 11 inches (28 centimeters) in width with tentacles that may reach a length of over 78 inches (2 meters) : sea wasp
Found in the waters off northern Australia, the box jellyfish … is not the only marine invertebrate to use venom, but it is the possessor of arguably the most lethal venom in the world. — Jamie Seymour