Article in craft herein (3)
I believe the answer is:
the
'article' is the definition.
(the definite article in English)
'in craft herein' is the wordplay.
'in' indicates the answer is hidden within the clue.
'THE' is hidden within 'craft herein'.
(Other definitions for the that I've seen before include "Born - - - - - - - - (carol)" , "See 10 Across" , "15, 16 One given taste of own medicine" , "Over - - moon" , "The most frequently occurring word in the Bible (and in this clue!)" .)