Swallow a mushroom in court (6)
I believe the answer is:
accept
'swallow' is the definition.
(thesaurus)
'a mushroom in court' is the wordplay.
'mushroom' becomes 'cep' (Boletus edulis - an edible mushroom).
'in' means one lot of letters goes inside another.
'court' becomes 'ct'.
'cep' put into 'ct' is 'ccept'.
'a'+'ccept'='ACCEPT'
(Other definitions for accept that I've seen before include "Receive willingly or take as true" , "Have belief in" , "Receive something proffered" , "Take on (responsibility)" , "Receive what's offered" .)