Upside down cakes put down (4)
I believe the answer is:
snub
'put down' is the definition.
(thesaurus)
'upside down cakes' is the wordplay.
'upside down' says the letters should be written in reverse.
'cakes' becomes 'buns' (I've seen this before).
'buns' reversed gives 'SNUB'.
(Other definitions for snub that I've seen before include "Cold-shoulder" , "Spurn; (of nose) turned up at the end" , "Reject a person with cold behaviour" , "'Rebuff, ignore (4)'" , "Ignore totally" .)