Bone from three in the reckoning? (7)
I believe the answer is:
sternum
'bone' is the definition.
(the breastbone)
'three in the reckoning?' is the wordplay.
I cannot quite see how this works, but
'three' could be 'ter' (see Chambers) and 'ter' is found within the answer.
This explanation may well be incorrect...
'from' is the link.
Can you help me to learn more?
(Other definitions for sternum that I've seen before include "front of breast" , "Human bone -- ten rums (anag)" , "Chest bone" , "Munster (anag.)" , "somewhere in chest" .)