Staple filling requires little relish (8)
I believe the answer is:
appetite
'relish' is the definition.
(thesaurus)
'staple filling requires little' is the wordplay.
'filling' indicates the central letters (the letters which fill the word).
'requires' means one lot of letters go next to another.
'little' becomes 'petite' (similar in meaning).
The central letters of 'staple' are 'ap'.
'ap'+'petite'='APPETITE'
(Other definitions for appetite that I've seen before include "Natural desire to satisfy a need" , "'Strong desire, craving (8)'" , "stomach" , "thirst" , "enthusiasm" .)