Supply vital input to support informative response (8)
I believe the answer is:
feedback
'informative response' is the definition.
(I've seen this before)
'supply vital input to support' is the wordplay.
'supply' becomes 'feed' (feeding is a kind of supplying).
'vital input' becomes 'back' (I can't justify this - if you can you should believe this answer much more).
'to support' says to put letters next to each other (in a down clue, some letters hold others up).
'feed'+'back'='FEEDBACK'
Can you help me to learn more?
(Other definitions for feedback that I've seen before include "Reaction" , "Responses to customer survey" , "useful response to inquiry" , "Return of product information to supplier" , "some whistling?" .)