Country air (6)
'country air?' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for national anthem that I've seen before include "The Marseillaise, perhaps" , "noted stirrer" , "The Star-Spangled Banner', say" , "country air" , "Patriotic song" .)
(Other definitions for anthem that I've seen before include "National tune" , "Religious chant" , "Choral work" , "National melody" , "Uplifting song -- the man (anag)" .)