a suffix of nouns denoting action or process, change, state or condition, etc., and corresponding to verbs ending in -esce or adjectives ending in -escent: convalescence; luminescence.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Word Origin and History for -escence
word-forming element meaning "process or state of being," from Latin -escentia, from -escentem (see -escent).
Online Etymology Dictionary, © 2010 Douglas Harper