A brief vote in favour? Indeed (3)
I believe the answer is:
aye
'indeed' is the definition.
(I've seen this before)
'a brief vote in favour?' is the wordplay.
'brief' means to remove the last letter (a shorter or briefer version of the word).
'vote in favour?' becomes 'yea' (an affirmative vote, as in 'yea or nay').
'yea' with its final letter removed is 'ye'.
'a'+'ye'='AYE'
(Other definitions for aye that I've seen before include "Yes vote" , "Always" , "Yes answer in voting" , "Word of assent" , "Positive voting response" .)