Apparition revealed by good entertainer (5)
I believe the answer is:
ghost
'apparition' is the definition.
(ghost is a kind of apparition)
'good entertainer' is the wordplay.
'good' becomes 'g' (abbreviation).
'entertainer' becomes 'host' (person hosting or entertaining guests).
'g'+'host'='GHOST'
'revealed by' is the link.
(Other definitions for ghost that I've seen before include "Write for another" , "Spectre, wraith" , "author for someone" , "Supernatural apparition" , "Visible manifestation of a dead person" .)