Chew gum and eat bananas (9)
I believe the answer is:
masticate
'chew' is the definition.
('masticate' can be a synonym of 'chew')
'gum and eat bananas' is the wordplay.
'gum' becomes 'mastic' (mastic is a resin also called arabian gum).
'and' says to put letters next to each other.
'bananas' is an anagram indicator (informal term for mad).
'eat' anagrammed gives 'ate'.
'mastic'+'ate'='MASTICATE'
(Other definitions for masticate that I've seen before include "champ" , "Torpor" , "Chew food" , "Crush" , "deal with mouthful" .)