Ahi, for one (4)
I believe the answer is:
tuna
'ahi for one' 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 "Sea creature" , "Large edible sea fish, often canned" , "Marine food fish" , "Large sea-fish" , "Skipjack --, blue-fin --" .)