Endless task given to a learner associated with singing (6)
I believe the answer is:
choral
'singing' is the definition.
(thesaurus)
'endless task given to a learner associated with' is the wordplay.
'endless' means to remove the last letter.
'task' becomes 'chore' ('chore' can be a synonym of 'task').
'given to' means one lot of letters go next to another.
'learner' becomes 'l'.
'associated with' is a charade indicator (letters next to each other).
'chore' with its final letter taken off is 'chor'.
'chor'+'a'+'l'='CHORAL'
(Other definitions for choral that I've seen before include "Music for groups of singers" , "harmonious society" , "Involving many singers" , "Of a singing group" , "Sung by group of singers" .)