it becomes ef- before f; e- before b, d, g, j, l, m, n, r, or v; often ec- before c or s; and, in many words of French origin, es-
used in hyphenated compounds
ex-president, ex-convict, ex-wife
Webster’s New World College Dictionary, 4th Edition. Copyright © 2010 by
Houghton Mifflin Harcourt. All rights reserved.
Word origin of 'ex-'ME < OFr or L, akin to Gr ex-, exō-, ek- < IE base *eĝhs, out