Approach large bull (6)
I believe the answer is:
drivel
'bull' is the definition.
(thesaurus)
'approach large' is the wordplay.
'approach' becomes 'drive' (a driveway is an approach to a house).
'large' becomes 'L' (eg in clothes sizes).
'drive'+'l'='DRIVEL'
(Other definitions for drivel that I've seen before include "Foolish talk" , "Gibberish" , "Nonsense, garbage" , "Tosh" , "Spoken nonsense" .)