Such a proposal isnt on, it would seem (5)
I believe the answer is:
offer
'such a proposal' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for offer that I've seen before include "Pay increase" , "Volunteer, present" , "Volunteer -- proposal" , "Hold out, tender" , "Tender for acceptance" .)