Note to include zero as digit (3)
I believe the answer is:
toe
'digit' is the definition.
(toe is a kind of digit)
'note to include zero' is the wordplay.
'note' becomes 'te' (**).
'to include' indicates putting letters inside.
'zero' becomes 'o'.
'te' placed around 'o' is 'TOE'.
'as' is the link.
(Other definitions for toe that I've seen before include "Foot extremity." , "Calabria?" , "End of sock" , "Conform or obey; ... the line" , "Small member" .)