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 é-; as, escape, scape, élite. 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.  [1913 Webster]