Even reversing, I would be quick (5)
I believe the answer is:
rapid
'quick' is the definition.
(synonyms)
'even reversing i would' is the wordplay.
'even' becomes 'par' (I've seen this in other clues).
'reversing' says the letters should be written in reverse.
'i would' becomes 'I'd'.
'par' written backwards gives 'rap'.
'rap'+'id'='RAPID'
'be' acts as a link.
(Other definitions for rapid that I've seen before include "Fast, quick" , "Electrical connector" , "Quick or swift" , "Flying" , "Fleet, swift" .)