Nuts - crack almonds to start with (4)
I believe the answer is:
gaga
'nuts' is the definition.
(thesaurus)
'crack almonds to start with' is the wordplay.
'crack' becomes 'gag' (both can mean a joke).
'to start with' suggests taking the first letters.
The initial letter of 'almonds' is 'a'.
'gag'+'a'='GAGA'
(Other definitions for gaga that I've seen before include "Barmy joke, third in cracker" , "Slightly mad (colloq.)" , "Slangily crazy, off one's head" , "Doddery" , "Slangily crazy or senile" .)