Song is abomination without two altos (6)
I believe the answer is:
anthem
'song' is the definition.
(anthem is a kind of song)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for anthem that I've seen before include "One for doomed youth" , "Solemn song" , "National tune" , "Internationale?" , "air of patriotism?" .)