On in centre of graveyards: a mournful song (5)
I believe the answer is:
elegy
'a mournful song' is the definition.
(I've seen this before)
'on in centre of graveyards' is the wordplay.
'on' becomes 'leg' (cricket term, fielding positions).
'in' indicates putting letters inside.
'centre of' indicates the central letters.
The middle letters of 'graveyards' are 'ey'.
'leg' put into 'ey' is 'ELEGY'.
(Other definitions for elegy that I've seen before include "Poetic lament for the dead" , "Sorrowful poem/song" , "lines of regret" , "Work of poet" , "Sad work" .)