Fish only (4)
I believe the answer is:
sole
I believe this is a double definition.
'fish' is the first definition.
(I know that sole is a type of fish)
'only' is the second definition.
(I know that only can be written as sole)
(Other definitions for sole that I've seen before include "swimmer" , "Lone; part of foot" , "Bottom of the foot" , "Shoe part -- lone" , "A fish; part of shoe" .)