On reflection, I would sound absent-minded (8)
I believe the answer is:
distrait
'absent-minded' is the definition.
(I've seen this before)
'on reflection i would sound' is the wordplay.
'on reflection' says the letters should be written in reverse.
'i would' becomes 'I'd'.
'sound' becomes 'strait' (strait is a kind of sound).
'id' written backwards gives 'di'.
'di'+'strait'='DISTRAIT'
(Other definitions for distrait that I've seen before include "Preoccupied" , "Being one [SCATTY]" , "Inattentive or absent-minded, from French" , "Unable to concentrate for anxiety - it is trad (anag)" , "Distraught in France" .)