-ность

Etymology
Probably originated from the suffix added to words ending in, and was then extracted by  as a productive suffix. The same thing happened with e.g. and English.

Suffix

 * → (no such word *гото́вный exists, making it a special case.)
 * → (no such word *о́бщный exists)
 * → (no such word *о́бщный exists)

Usage notes

 * Not all words in contain this suffix. Most of them are formed from  added to adjectives in, e.g.  from.
 * As noted above, is the regular alternative to  after adjectives whose stem ends in щ, e.g., ,.