Band of singers or such at work (6)
I believe the answer is:
chorus
'band of singers' is the definition.
(a chorus is a group of singers)
'or such at work' is the wordplay.
'at work' indicates anagramming the letters.
'or'+'such'='orsuch'
'orsuch' is an anagram of 'CHORUS'.
(Other definitions for chorus that I've seen before include "Song part repeated after each verse" , "Group of voices" , "Organized group of singers" , "Some chanting" , "See 19" .)