Point to one that’s weak (3)
I believe the answer is:
'weak' is the definition.
(similar in meaning)
'point to one' is the wordplay.
'point' becomes 'w' (W is an example).
'to one' becomes 'an' (I've seen this in other clues).
'that's' acts as a link.
(Other definitions for wan that I've seen before include "Pale and ill-looking" , "Pale and peaky" , "Pasty" , "Direly pale" , "Lacking colour" .)