Discovered limitless pocket (4)
I believe the answer is:
earn
'pocket' is the definition.
(I've seen this in another clue)
'discovered limitless' is the wordplay.
'discovered' becomes 'learnt' (I've seen this in another clue).
'limitless' means to look at the middle letters.
The middle of 'learnt' is 'EARN'.
(Other definitions for earn that I've seen before include "make bread?" , "Gain, take in" , "Attain" , "Deserve - merit" , "Gain by work or effort" .)