Longman Dictionary of Contemporary English
The Collaborative International Dictionary
Ex- \Ex-\ A prefix from the latin preposition, ex, akin to Gr. 'ex or 'ek signifying out of, out, proceeding from. Hence, in composition, it signifies out of, as, in exhale, exclude; off, from, or out, as in exscind; beyond, as, in excess, exceed, excel; and sometimes has a privative sense of without, as in exalbuminous, exsanguinous. In some words, it intensifies the meaning; in others, it has little affect on the signification. It becomes ef- before f, as in effuse. The form e- occurs instead of ex- before b, d, g, l, m, n, r, and v, as in ebullient, emanate, enormous, etc. In words from the French it often appears as es-, sometimes as s- or ['e]-; as, escape, scape, ['e]lite. Ex-, prefixed to names implying office, station, condition, denotes that the person formerly held the office, or is out of the office or condition now; as, ex-president, ex-governor, ex-mayor, ex-convict. The Greek form 'ex becomes ex in English, as in exarch; 'ek becomes ec, as in eccentric.
Douglas Harper's Etymology Dictionary
word-forming element, in English meaning usually "out of, from," but also "upwards, completely, deprive of, without," and "former;" from Latin ex "out of, from within," from PIE *eghs "out" (cognates: Gaulish ex-, Old Irish ess-, Old Church Slavonic izu, Russian iz). In some cases also from Greek cognate ex, ek. PIE *eghs had comparative form *eks-tero and superlative *eks-t(e)r-emo-. Often reduced to e- before -b-, -d-, -g-, consonantal -i-, -l-, -m-, -n-, -v- (as in elude, emerge, evaporate, etc.).
pre. 1 out of 2 outside 3 former, but still living (qualifier: almost always used with a hyphen) 4 (context biology English) Lacking.
Usage examples of "ex-".
We're fabbing the wing in Atlanta so that the senator from Georgia will stop messing with us every time we go to the Ex-Im Bank for a big loan.