Slim regularly, or need quiche (6)
I believe the answer is:
reduce
'slim' is the definition.
(synonyms)
'regularly or need quiche' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'or'+'need'+'quiche'='orneedquiche'
The alternating letters of 'orneedquiche' are 'REDUCE'.
(Other definitions for reduce that I've seen before include "Cut down, lose weight" , "Slim down or discount" , "Pare" , "Make smaller or take off weight" , "subdue" .)