Set of furniture used by engineers during the quiet course, say (5,5,5)
I believe the answer is:
three piece suite
'say' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'set of furniture used by engineers during the quiet course' is the wordplay.
'set of furniture' becomes 'suite' (I've seen this before).
'used by' is a charade indicator (letters next to each other).
'engineers' becomes 're' (Royal Engineers).
'during' indicates putting letters inside.
'quiet course' becomes 'piece' (I can't explain this - if you can you should give a lot more credence to this answer).
're' put into 'the' is 'three'.
'three'+'piece'='threepiece'
'suite' put after 'threepiece' is 'THREE-PIECE SUITE'.
Can you help me to learn more?
(Another definition for three piece suite that I've seen is " seats".)