Ladder rung (4)
I believe the answer is:
step
'ladder rung' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for step that I've seen before include "Pace - part of a procedure" , "Manner of walking" , "Bit of mashed potato maybe" , "Rung, dance movement" , "Place foot on as with a pest" .)