Employ part of Halloween gag explicitly (6)
I believe the answer is:
engage
'employ' is the definition.
(I've seen this before)
'part of halloween gag explicitly' is the wordplay.
'part of' says the answer is hidden in the clue.
'ENGAGE' is hidden in the letters of 'halloween gag explicitly'.
(Other definitions for engage that I've seen before include "Join" , "Employ or captivate" , "Secure" , "Employ as a worker" , "Take into service or commit to marriage" .)