box jellyfish

noun

variants or less commonly box jelly

: any of various cube-shaped jellyfishes (class Cubozoa) 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

Examples of box jellyfish in a Sentence

Recent Examples on the Web

The sting of the Australian box jellyfish has been described as being lashed with a whip dipped in burning acid, and is powerful enough to kill an adult in as little as two minutes! — New Atlas, 30 June 2026

Many box jellyfish species primarily inhabit mangrove lagoons, which provide abundant prey and shelter. — Scott Travers, Forbes.com, 4 June 2026

Irukandji jellyfish is reportedly a type of box jellyfish. — Gabrielle Rockson, PEOPLE, 22 Apr. 2026

The Australian box jellyfish is considered the most venous marine animal in the world, according to the National Oceanic and Atmospheric Administration (NOAA). — Taryn White, Travel + Leisure, 29 Oct. 2025

Word History

Etymology

from its square shape

First Known Use

1960, in the meaning defined above

Rhymes for box jellyfish

• bluefish
• catfish
• codfish
• crawfish
• dogfish
• finfish
• flatfish
• goldfish
• groundfish
• kingfish
• offish
• redfish

Medical Definition

box jellyfish

noun

: sea wasp