Eight-armed creature (7)
'eight-armed creature' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for octopus that I've seen before include "one that's heavily armed?" , "Tentacled marine mollusc" , "Scoot up (anag.)" , "Eight-limbed cephalopod" , "Ocean-dweller" .)
(Other definitions for octopod that I've seen before include "Eight-legged creature" , "Eight-armed/footed" , "mollusc" , "Eight-limbed creature" .)