IPA: /ˈsteɪbəl.nəs/
KK: /ˈsteɪbəlnəs/
The quality of being steady and not changing; the state of being stable.
The stableness of the bridge was tested before it was opened to traffic.
Stableness is formed from "stable" (from Latin "stabilis", meaning firm or steady) and the suffix "-ness" (meaning the state or quality of). The word "stableness" refers to the quality of being stable or firm.
Think of 'stable' as something that is firm and steady, and remember that 'stableness' means the quality of being stable.