Gaps in bone plugged by operation (9)
I believe the answer is:
omissions
'gaps' is the definition.
(eg gaps in a list)
'bone plugged by operation' is the wordplay.
'bone' becomes 'os' (Latin for 'bone').
'plugged by' is an insertion indicator (plug can mean to block up a gap).
'operation' becomes 'mission' (mission is a kind of operation).
'os' going around 'mission' is 'OMISSIONS'.
'in' acts as a link.
(Other definitions for omissions that I've seen before include "Defaults" , "Have they been left out" , "mistakes" .)