Bone usually located near adductor initially (4)
I believe the answer is:
ulna
'bone' is the definition.
(ulna is a kind of bone)
'usually located near adductor initially' is the wordplay.
'initially' indicates taking the first letters.
The initial letters of 'usually located near adductor' is 'ULNA'.
(Other definitions for ulna that I've seen before include "Part of body" , "Uneven" , "Car document; ticket book" , "Part of bone-structure" , "structural member?" .)