Personal ambition to store meat (4)
I believe the answer is:
'meat' is the definition.
(I know that lamb is a type of meat)
'personal ambition to store' is the wordplay.
'to store' indicates a hidden word (I've seen 'stores' mean this).
'LAMB' is hidden within 'personal ambition'.
(Other definitions for lamb that I've seen before include "Tender sheep meat" , "Mary, and Charles?" , "Young sheep" , "Meekest" , "Young farm animal" .)