Some began The Mikado song (6)
I believe the answer is:
anthem
'song' is the definition.
(anthem is a kind of song)
'some began the mikado' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'ANTHEM' is hidden within 'began the mikado'.
(Other definitions for anthem that I've seen before include "air of patriotism?" , "Church choral piece" , "One for doomed youth" , "National tune" , "Solemn song" .)