the.com/rung

means One of the horizontal bars on a ladder (or a similar supporting crosspiece) that you place your foot or hand on to climb — and by extension, a level in a hierarchy or career.

from From Old English 'hrung,' meaning a rod, bar, or crossbar — part of a very old Germanic word family (related to German 'Runge,' a cart's stake or bar). It originally just meant any sturdy wooden crosspiece, not specifically a ladder's step; the ladder sense narrowed from that general 'bar' meaning over time, and the metaphorical 'rung of the ladder of success' came later still.