Without nurse regularly around, must reset bone (7)
I believe the answer is:
sternum
'bone' is the definition.
(the breastbone)
'without nurse regularly around must reset' is the wordplay.
'without' means one lot of letters goes inside another.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'around' indicates an anagram.
'reset' indicates an anagram.
The alternate letters of 'nurse' are 'nre'.
'nre' with letters rearranged gives 'ern'.
'must' with letters rearranged gives 'stum'.
'ern' put inside 'stum' is 'STERNUM'.
(Other definitions for sternum that I've seen before include "big bone" , "Human bone -- ten rums (anag)" , "Munster (anag.)" , "front of breast" , "somewhere in chest" .)