Collect a large amount (5)
I believe the answer is:
amass
'collect' is the definition.
(I know that collect can be written as amass)
'a large amount' is the wordplay.
'large amount' becomes 'mass' (I've seen this in another clue).
'a'+'mass'='AMASS'
(Other definitions for amass that I've seen before include "store" , "Build up" , "Get together" , "Accumulate, pile up" , "Collect or gather" .)