Collect a great deal (5)
I believe the answer is:
amass
'collect' is the definition.
(synonyms)
'a great deal' is the wordplay.
'great deal' becomes 'mass' (synonyms).
'a'+'mass'='AMASS'
(Other definitions for amass that I've seen before include "Put together" , "Accrue, heap up" , "Build up" , "Gathers" , "store" .)