-ость

Etymology
From. Some authors claim that the suffix is merged from double suffixation, but there is a lot of evidence that suffix  already existed in Late Proto-Slavic. Also, compare 🇨🇬.

Suffix

 * 1) -ness, -ity; deadjectival nominalizing suffix used to create an i-stem feminine noun, usually an abstract noun denoting a quality.
 * 2) * &rarr;
 * 3) * &rarr;
 * 4) * &rarr;
 * 5) * &rarr;
 * 6) * &rarr;
 * 7) * &rarr;

Usage notes
When attached to a soft (palatal) stem, the variant is used.

Etymology
.

Suffix

 * 1) -ness, -ity