-ibly

Etymology
Euphonic, due to difficulty of pronouncing *-iblely. Compare same sound change in unrelated, , and.

Suffix

 * audible &rarr; audibly
 * audible &rarr; audibly

Usage notes
As with, generally only used to form analogs to adjectives ending in , replacing the existing suffix (respectively ). Rather than a distinct suffix, this can be considered a class of euphonic blends of “-ble” and, as in , , and , among others.

Further, as with, generally unproductive as an suffix to existing English words – most words ending in are derived from words ending in  borrowed from Latin or Old/Middle French, not formed by suffixing in English. Productive uses in English include.