Infatuate thus in punt (5)
I believe the answer is:
besot
'infatuate' is the definition.
(I've seen this in another clue)
'thus in punt' is the wordplay.
'thus' becomes 'so' (synonyms).
'in' indicates putting letters inside.
'punt' becomes 'bet' (I've seen this in other clues).
'so' inserted into 'bet' is 'BESOT'.
(Other definitions for besot that I've seen before include "Make stupid" , "Stupefy, make silly or foolish" , "Make love" .)