One cutting into roast creates bother (4)
I believe the answer is:
pain
'bother' is the definition.
(I know that bother can be written as pain)
'one cutting into roast' is the wordplay.
'one' becomes 'i' (Roman numeral).
'cutting into' means one lot of letters goes inside another.
'roast' becomes 'pan' (panning roast is a kind of roasting).
'i' inserted into 'pan' is 'PAIN'.
'creates' is the link.
(Other definitions for pain that I've seen before include "nuisance to be put up with" , "great discomfort" , "French bread?" , "Physical discomfort" , "Suffering, ache" .)