Pedometer unit (4)
I believe the answer is:
step
'pedometer unit' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for step that I've seen before include "Prefix meaning related by remarriage" , "Pace - part of a procedure" , "Footprint" , "Stair" , "Rung, dance movement" .)