a noun suffix, equivalent to -ence: consistency; dependency; exigency.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for -ency
suffix forming nouns
a variant of -ence fluency; permanency
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Word Origin and History for -ency
word-forming element denoting quality or state, from Latin -entia. Derivatively identical with -ence.
Online Etymology Dictionary, © 2010 Douglas Harper