Cutting remarks, principally in bar (7)
I believe the answer is:
excerpt
'cutting' is the definition.
(something extracted or cut from a text)
'remarks principally in bar' is the wordplay.
'principally' says to take the initial letters.
'in' is an insertion indicator.
'bar' becomes 'except' (both can mean 'not including').
The initial letter of 'remarks' is 'r'.
'r' placed within 'except' is 'EXCERPT'.
(Other definitions for excerpt that I've seen before include "a little" , "Selected passage from larger work" , "Selection, extract" , "Short passage" , "Textual passage" .)