giant octopus

Noun

Meaning

A mythical or fictional large sea creature with features of an octopus
(informal) Synonym of Kraken (Norse sea monster)

(informal) Synonym of Cthulhu (Lovecraftian horror monster)

One of certain large sea creatures of the order Octopoda
Haliphron atlanticus (giant Atlantic octopus)

Enteroctopus spp.
especially, Enteroctopus dofleini (giant Pacific octopus)

Source: en.wiktionary.org