Get together in a service (5)
I believe the answer is:
amass
'get together' is the definition.
(I've seen this before)
'a service' is the wordplay.
'service' becomes 'mass' (I've seen this in other clues).
'a'+'mass'='AMASS'
'in' is the link.
(Other definitions for amass that I've seen before include "Gathers" , "Collect or gather" , "Put together" , "store" , "Accumulate, pile up" .)