Mentioned calm composition? (5)
I believe the answer is:
piece
'composition?' is the definition.
(I know that composition can be written as piece)
'mentioned calm' is the wordplay.
'mentioned' indicates a 'sounds like' (homophone) clue.
'calm' becomes 'peace' (peaceful situation).
'peace' sounds like 'PIECE'.
(Other definitions for piece that I've seen before include "that may follow show after work party?" , "Portion; musical work" , "artefact" , "Artwork" , "Section; firearm" .)