Webster's Dictionary 
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.
King James Dictionary 
Ex. A Latin preposition or prefix, Gr. signifying out of, out, proceeding from. Hence in composition, it signifies sometimes out of, as in exhale, exclude sometimes off, from or out, as in L. excindo, to cut off or out sometimes beyond, as in excess, exceed, excel. In some words it is merely emphatical in others it has little effect on the signification.