Less to be covered by you once son is booming (10)
I believe the answer is:
thunderous
'is booming' is the definition.
(thesaurus)
'less to be covered by you once son' is the wordplay.
'less' becomes 'under' (I've seen this in other clues).
'to be covered by' means one lot of letters goes inside another.
'you once' becomes 'thou' (historical second person pronoun).
'son' becomes 's' (genealogical abbreviation for son).
'under' placed into 'thou' is 'thunderou'.
'thunderou'+'s'='THUNDEROUS'
(Other definitions for thunderous that I've seen before include "Deafening" , "Loud and rumbling" .)