Bury girl, one on break (12)
I believe the answer is:
'break' is the definition.
(I know that break can be written as intermission)
'bury girl one on' is the wordplay.
'bury' becomes 'inter' (to inter is to put into the ground).
'girl' becomes 'mission' (I can't justify this - if you can you should believe this answer much more).
'one on' means one lot of letters go next to another.
(Other definitions for intermission that I've seen before include "Theatre's half-time" , "Interval" , "Entr'acte" , "Pause, break" , "Break; respite" .)