giant octopus

Short definition from Wiktionary

Noun

1. 1
   A mythical or fictional large sea creature with features of an octopus: Synonym of Kraken (Norse sea monster)
2. 2
   A mythical or fictional large sea creature with features of an octopus: Synonym of Cthulhu (Lovecraftian horror monster)
3. 3
   One of certain large sea creatures of the order Octopoda: Haliphron atlanticus (giant Atlantic octopus)
4. 4
   One of certain large sea creatures of the order Octopoda: Enteroctopus spp.
5. 5
   Enteroctopus spp: especially, Enteroctopus dofleini (giant Pacific octopus)