Support in setting up dinner (8)
I believe the answer is:
underpin
'support' is the definition.
(underpinning is a kind of supporting)
'setting up dinner' is the wordplay.
'setting' indicates an anagram.
'up'+'dinner'='updinner'
'updinner' is an anagram of 'UNDERPIN'.
'in' acts as a link.
(Other definitions for underpin that I've seen before include "corroborate" , "buttress" , "Prop up with nun pride" , "Support or strengthen from beneath" , "Form the basis for" .)