Good to enter better digit (6)
I believe the answer is:
finger
'digit' is the definition.
('finger' can be a synonym of 'digit')
'good to enter better' is the wordplay.
'good' becomes 'g' (abbreviation).
'to enter' indicates putting letters inside.
'better' becomes 'finer'.
'g' inserted within 'finer' is 'FINGER'.
(Other definitions for finger that I've seen before include "Index" , "Feel" , "Part of one's 10" , "shop" , "Tell the cops" .)