Enthusiast boxes in this way (4)
I believe the answer is:
thus
'in this way' is the definition.
('thus' can be a synonym of 'in this way')
'enthusiast boxes' is the wordplay.
'boxes' says the answer is hidden in the clue (to box can mean to contain).
'THUS' is hidden within 'enthusiast'.
(Other definitions for thus that I've seen before include "As a result" , "Shut (anag.)" , "Like so" , "In this way" , "an original Christmas gift" .)