Roar (6)
'roar' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for bellow that I've seen before include "Shout; Saul --, novelist" , "author" , "Roar loudly" , "Loud cry of a bull" , "Loud and deep roar" .)
'roar' is the definition.
(thundering is a kind of roaring)
This is all the clue.
(Other definitions for thunder that I've seen before include "Roar" , "Red hunt for a loud noise" , "Noise heard after lightning" , "Weather featuring with 1" , "Meteorological rumblings" .)