Feeling it's a key proposal (7)
I believe the answer is:
emotion
'feeling' is the definition.
(I know that emotion is a type of feeling)
'a key proposal' is the wordplay.
'a key' becomes 'e' (a musical key).
'proposal' becomes 'motion' (proposal at a meeting).
'e'+'motion'='EMOTION'
'it's' is the link.
(Other definitions for emotion that I've seen before include "Feeling like love or fear" , "sense" , "Strong desire" , "Surprise, perhaps" , "Strong feeling of joy, fear etc" .)