Octopus's home (3)
I believe the answer is:
sea
'octopus's home' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sea that I've seen before include "Adriatic, for example" , "The drink" , "All at . . . - totally confused" , "Expanse of salt water" , "Cod's home?" .)