Note the old-fashioned watch (3)
I believe the answer is:
eye
'watch' is the definition.
(eye can mean to watch or look at)
'note the old-fashioned' is the wordplay.
'note' becomes 'e' (musical note).
'the old-fashioned' becomes 'ye' (resembles a historical spelling of 'the').
'e'+'ye'='EYE'
(Other definitions for eye that I've seen before include "Four [NEEDLEFUL] may pass through this" , "Globular organ" , "Aperture" , "potato bud" , "Place for pupil" .)