Supports suggestion not to finish bottom (8)
I believe the answer is:
backside
'bottom' is the definition.
(I know that bottom can be written as backside)
'supports suggestion not to finish' is the wordplay.
'supports' becomes 'backs' ('back' can be a synonym of 'support').
'suggestion' becomes 'idea' (I've seen this before).
'not to finish' means to remove the last letter.
'idea' with its final letter taken off is 'ide'.
'backs'+'ide'='BACKSIDE'
(Other definitions for backside that I've seen before include "Bottom" , "Rear" , "Seat" , "Hind part" , "Buttocks" .)