The most common and most likely answer to this crossword clue is the 8 letter word SIBELIUS
S
I
B
E
L
I
U
S
More clues leading to the result SIBELIUS
- One composer or another wanting daughter to support sibling
- Encore rejected – missing start of another theme word
- Brother perhaps joined priest and American composer
- Symphonist, British, is turning up with English composer needing no introduction
- Composer‘s relative replacing another composer’s intro
- Composer having suspicion about one? Deny cut
Buddy explains!

The straight part
We know that "Composer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case composer = sibelius.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.