Leitmotiv Keith Emerson embodies (5)
I believe the answer is:
theme
'leitmotiv' is the definition.
(I've seen this before)
'keith emerson embodies' is the wordplay.
'embodies' indicates the answer is hidden within the clue.
'THEME' is hidden within 'keith emerson'.
(Other definitions for theme that I've seen before include "Melody on which variations are constructed" , "tune used in Enigma Variations?" , "Topic, leitmotif" , "issue" , "Subject; recurring idea" .)