Bone queen buried in compost (7)
I believe the answer is:
humerus
'bone' is the definition.
(humerus is a kind of bone)
'queen buried in compost' is the wordplay.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'buried in' means one lot of letters goes inside another.
'compost' becomes 'humus' (I've seen this before).
'er' inserted within 'humus' is 'HUMERUS'.
(Other definitions for humerus that I've seen before include "Bone from shoulder to elbow" , "Boneo of the upper arm" , "Upper arm bone" , "Bone that sounds funny?" , "What's often thought funny" .)