Lively part of Macbeth where apparitions are summoned, ending in massacre (6)
I believe the answer is:
active
'lively' is the definition.
(similar in meaning)
'part of macbeth where apparitions are summoned ending in massacre' is the wordplay.
'part of macbeth where apparitions are summoned' becomes 'activ' (Act IV of Shakespeare's Macbeth).
'ending in' indicates one should take the final letters.
The last letter of 'massacre' is 'e'.
'activ'+'e'='ACTIVE'
(Other definitions for active that I've seen before include "Dynamic, functioning" , "(Of mind) alert, lively" , "Industrious" , "Moving, doing things" , "Not passive" .)