Offer of support also set out (8)
I believe the answer is:
proposal
'offer' is the definition.
(I know that proposal is a type of offer)
'support also set out' is the wordplay.
'support' becomes 'prop' (prop up can mean to support).
'set out' indicates anagramming the letters.
'also' anagrammed gives 'osal'.
'prop'+'osal'='PROPOSAL'
'of' is the link.
(Other definitions for proposal that I've seen before include "Offer, of marriage say" , "Plan, suggestion" , "Offer - suggestion" , "put before the union?" , "a match might be arranged?" .)