A group heard to accumulate (6)
I believe the answer is:
accrue
'to accumulate' is the definition.
(I've seen this in another clue)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for accrue that I've seen before include "(Of money) be received in increasing amounts" , "Grow by addition" , "Accumulate or amass like interest" , "Grow like interest on capital" , "Increase by periodic additions" .)