Musical section briefly captivating royal 2 (6)
I believe the answer is:
brahms
'2' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'musical section briefly captivating royal' is the wordplay.
'musical' becomes 'bra' (I can't justify this - if you can you should believe this answer much more).
'section briefly' becomes 's' (legal abbreviation; 'briefly' suggests an abbreviation).
'captivating' is an insertion indicator (I've seen this in other clues).
'royal' becomes 'hm' (His or Her Majesty).
'bra'+'s'='bras'
'bras' going around 'hm' is 'BRAHMS'.
Can you help me to learn more?
(Other definitions for brahms that I've seen before include "Half-drunk composer" , "Johannes -, nineteenth century German composer" , "German barman" , "German scorer" , "Musician" .)