Rebellious chorister lacking special eloquence (8)
I believe the answer is:
rhetoric
'eloquence' is the definition.
(thesaurus)
'rebellious chorister lacking special' is the wordplay.
'rebellious' indicates an anagram.
'lacking' suggests deleting specific letters.
'special' becomes 's' (common abbreviation as in Special Air Service).
'chorister' with 's' removed is 'choriter'.
'choriter' with letters rearranged gives 'RHETORIC'.
(Other definitions for rhetoric that I've seen before include "Art of using language for persuasion" , "Art of impressive public speaking" , "Art of persuasive use of words" , "pomposity" , "Torchier with language of orator" .)