Collects a great deal (7)
I believe the answer is:
amasses
'collects' is the definition.
('amass' can be a synonym of 'collect')
'a great deal' is the wordplay.
I cannot quite understand how this works, but
'a' is present in the answer.
'deal' could be 'mass' (synonyms) and 'mass' is found within the answer.
The remaining letters 'es' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for amasses that I've seen before include "Gathers together" , "Collects" , "'Accumulates, gathers (7)'" .)