Mark part of the intestine (5)
I believe the answer is:
colon
I believe this clue is a double definition.
'mark' is the first definition.
(I know that colon is a type of punctuation)
'part of the intestine' is the second definition.
(I know that colon is part of large intestine)
(Other definitions for colon that I've seen before include "cash" , "City at the Caribbean entrance to the Panama Canal" , "Panamanian port" , "Stop (less than full)" , "Stop (on the inside!)" .)