One rants madly, booming (8)
I believe the answer is:
resonant
'booming' is the definition.
(I've seen this before)
'one rants madly' is the wordplay.
'madly' indicates anagramming the letters.
'one'+'rants'='onerants'
'onerants' with letters rearranged gives 'RESONANT'.
(Other definitions for resonant that I've seen before include "Like" , "Tending to prolong sound, echoing" , "Deep and vibrating" , "Deep, clear and continuing to sound or reverberate" , "Reverberating" .)