Thunderous applause? (4)
I believe the answer is:
clap
'applause?' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for clap that I've seen before include "Pat" , "Sudden loud noise (of thunder?)" , "express approval" , "Make sound of applause" , "Audibly show approval" .)