Unemployed lad primarily tucking into fish (4)
I believe the answer is:
idle
'unemployed' is the definition.
(similar in meaning)
'lad primarily tucking into fish' is the wordplay.
'primarily' says to take the initial letters.
'tucking into' means one lot of letters goes inside another.
'fish' becomes 'ide' (type of fish).
The initial letter of 'lad' is 'l'.
'l' going within 'ide' is 'IDLE'.
(Other definitions for idle that I've seen before include "having been taken from service" , "Turn over" , "-- Jack, pantomime character" , "Loaf" , "Lazy - unemployed" .)