The most common and most likely answer to this crossword clue is the 12 letter word COUNTERPOINT
I've seen this crossword clue in The Daily Telegraph
C
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Buddy explains!
The straight part
We know that "Combination of melodies" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case combination of melodies = counterpoint.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.
What does COUNTERPOINT mean?
COUNTERPOINT noun- A melody added to an existing one, especially one added to provide harmony whilst each retains its simultaneous identity; a composition consisting of such contrapuntal melodies.
- Any similar contrasting element in a work of art.
- An opposite point.
- To compose or arrange such music.
- To serve as an opposing point against.
- The topmost covering of a bed, often functioning as a blanket; a coverlet.