Segment of the debacle from The Sound of Music perhaps (4)
I believe the answer is:
Here is my best explanation:
'segment' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'the debacle from the sound of music perhaps' is the subsidiary indication.
'clef' is hidden in amongst the letters.
However, I am not sure how this is indicated.
'of' is the link.
(Other definitions for clef that I've seen before include "Sign at start of stave", "Music pitch symbol", "Musical pitch notation", "that's marking the pitch", "Stave character", "Symbol on a stave indicating pitch", "Musical stave sign", "The pitch", "Mark determining musical pitch of notes" and "Musical symbol indicating pitch".)