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 exalbuminuos, 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, elite. 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.