階

Originally the stone platforms or steps placed at the front and back of a traditional building.

A phono-semantic compound:

阜 (“mound, hill, terrace”) provides the semantic element, relating to elevated structures.

皆 (gye/gae, “all”) provides the phonetic element.

階段 (계단) – stairs, stairway;

階級 (계급) – class, rank, social status;

階層 (계층) – stratum, level, social layer;

上階 (상계) – upper floor, higher rank;

下階 (하계) – lower floor, lower rank.

In traditional East Asian architecture, 階 referred specifically to stone steps at the front and back of a house or hall.

Over time, its meaning expanded metaphorically to include hierarchical levels, both physical (stairs, floors) and social (ranks, classes).

In Japanese usage, 階 (かい kai) is the common counter for “floor/story” of buildings (e.g., 二階 = second floor).