Part of a foot
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
inch
'part of a foot' is the definition.
(I know this)
This is all the clue.
(Other definitions for inch that I've seen before include "Subdivision of 14 down" , "Edge slowly" , "Linear measure" , "Measure - small island - move slowly" , "Move by slow degrees" .)