Admonition, it seems, about breaking into song (12)
I believe the answer is:
chastisement
'admonition' is the definition.
(thesaurus)
'it seems about breaking into song' is the wordplay.
'about' is an anagram indicator.
'breaking into' means one lot of letters goes inside another.
'song' becomes 'chant' (song sung by a crowd).
'it'+'seems'='itseems'
'itseems' anagrammed gives 'stiseme'.
'stiseme' inserted within 'chant' is 'CHASTISEMENT'.
(Other definitions for chastisement that I've seen before include "Old fashioned discipline" , "Severe reprimand" , "Beating" .)