Give a hand to catch bull (8)
I believe the answer is:
claptrap
'bull' is the definition.
(both can mean nonsense or rubbish)
'give a hand to catch' is the wordplay.
'give a hand to' becomes 'clap' (to give a hand is to give a round of applause).
'catch' becomes 'trap' (trapping is a kind of catching).
'clap'+'trap'='CLAPTRAP'
(Other definitions for claptrap that I've seen before include "High-sounding nonsense" , "Utter rubbish" , "Pretentious talk or nonsense" , "Meaningless nonsense" , "Meaningless, insincere or pompous talk" .)