Metaphor for a promotion (4)
I believe the answer is:
rung
'metaphor for a promotion' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rung that I've seen before include "support for foot" , "Step up the ladder - called for" , "Level in a hierarchy" , "Part of a ladder" , "Horizontal bar in ladder" .)