Deep bellows (5)
I believe the answer is:
roars
'deep bellows' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for roars that I've seen before include "Sounds like a lion" , "'Deep, bellowing bursts of sound (5)'" , "Deep bellows" , "Bellows, hollers" , "Bellows like a bull" .)