IPA: /ˈstɛrkeɪs/
KK: /ˈstɛrˌkeɪs/
A set of steps that allows people to move from one level of a building to another.
She walked up the staircase to reach the second floor.
Staircase → It is formed from "stair" (from Old English *stæger*, meaning a step or series of steps) and "case" (from Old French *casse*, meaning a box or container). The word "staircase" refers to a structure that contains a series of steps, allowing movement between different levels.
Think of a 'series of steps' ('stair') contained within a 'box' or structure ('case') — that's what a staircase is.
No commonly confused words.