Mile or mole
I believe the answer is:
unit
'mile or mole' is the definition.
(I know that Roman mile is a type of linear measure)
This is the entire clue.
(Other definitions for unit that I've seen before include "Individual thing or group regarded as complete" , "Entity making up part of a whole" , "Whole - group" , "Single piece - kitchen cabinet" , "Any division of quantity accepted as a standard of measurement" .)