Albacore (4)
I believe the answer is:
tuna
'albacore' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tuna that I've seen before include "Common food fish" , "Large salt water fish" , "Large edible sea fish, often canned" , "Large fish found in a nut" , "Type of fish" .)