Lofty aggregate providing this service (4,4)
I believe the answer is:
high mass
'this service' is the definition.
(I've seen this before)
'lofty aggregate' is the wordplay.
'lofty' becomes 'high' (similar in meaning).
'aggregate' becomes 'mass' (synonyms).
'high'+'mass'='HIGH MASS'
'providing' is the link.
(Other definitions for high mass that I've seen before include "full service" , "Church service celebrated with music, incense etc" .)