Unaccompanied small arias (5)
I believe the answer is:
solos
'arias' is the definition.
(I've seen this in another clue)
'unaccompanied small' is the wordplay.
'unaccompanied' becomes 'solo' (I've seen this before).
'small' becomes 's' (abbreviation - e.g. clothes size).
'solo'+'s'='SOLOS'
(Other definitions for solos that I've seen before include "Unaccompanied parts" , "Musical passages for one instrument" , "Numbers" , "Pieces of music for one voice or instrument" , "Passages for one player" .)