Donor somehow keeps workers' group booming (7)
I believe the answer is:
orotund
'booming' is the definition.
(synonyms)
'donor somehow keeps workers' group' is the wordplay.
'somehow' indicates an anagram.
'keeps' indicates putting letters inside.
'workers' group' becomes 'tu' (I've seen this in other clues).
'donor' is an anagram of 'orond'.
'orond' going around 'tu' is 'OROTUND'.
(Other definitions for orotund that I've seen before include "Loud or pompous" , "Of speech, dignified and pompous" , "booming" , "Resonant" , "Sonorous; pompous" .)