Offer support also, surprisingly (8)
I believe the answer is:
proposal
'offer' is the definition.
(proposal is a kind of offer)
'support also surprisingly' is the wordplay.
'support' becomes 'prop' (prop is a kind of support).
'surprisingly' indicates anagramming the letters.
'also' with letters rearranged gives 'osal'.
'prop'+'osal'='PROPOSAL'
(Other definitions for proposal that I've seen before include "A suggestion, perhaps of marriage" , "Offer, of marriage say" , "motion" , "Offer - suggestion" , "Suggestion put forward for consideration" .)