Bore I'm interrupting to put off (8)
I believe the answer is:
diameter
'bore' is the definition.
(thesaurus)
'i'm interrupting to put off' is the wordplay.
'i'm' becomes 'iam' (I've seen this in other clues).
'interrupting' indicates putting letters inside.
'to put off' becomes 'deter' (I've seen this before).
'iam' put inside 'deter' is 'DIAMETER'.
(Other definitions for diameter that I've seen before include "A demerit for line bisecting a circle" , "Calibre" , "It crosses the circle at its widest" , "Paying back (of money)" , "width of bar" .)