Trace bones, say (4)
I believe the answer is:
dreg
'trace' is the definition.
(I've seen this before)
'bones say' is the wordplay.
'bones' becomes 'dr' (I've seen this in other clues).
'say' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'dr'+'eg'='DREG'
(Other definitions for dreg that I've seen before include "Small amount left over" , "Small quantity (of residue?)" , "Trace" .)