Cellist initially plays moving love song (7)
I believe the answer is:
calypso
'song' is the definition.
(thesaurus)
'cellist initially plays moving love' is the wordplay.
'initially' indicates taking the first letters.
'moving' indicates an anagram.
'love' becomes 'o' (In tennis, 'love' means 'zero').
The initial letter of 'cellist' is 'c'.
'plays' with letters rearranged gives 'alyps'.
'c'+'alyps'+'o'='CALYPSO'
(Other definitions for calypso that I've seen before include "Improvised song of the Caribbean" , "West Indian song with variable rhythm and improvised words" , "W. Indian ballad" , "Slay cop with a West Indian song" , "who detained Odysseus?" .)