Used from mid-14c. in non-religious situations, "one who has forsaken the party, opinion, etc., to which he previously adhered."
It forms all or part of: advocate; avocation; calliope; convocation; epic; equivocal; equivocation; evoke; invoke; provoke; revoke; univocal; vocabulary; vocal; vocation; vocative; vociferate; vociferous; voice; vouch; vox; vowel.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit vakti "speaks, says," vacas- "word;" Avestan vac- "speak, say;" Greek eipon (aorist) "spoke, said," epos "word;" Latin vocare "to call," vox "voice, sound, utterance, language, word;" Old Prussian wackis "cry;" German er-wähnen "to mention."
"In early Greek mythology, the spirit of revenge, that prompts the members of a family to commit fresh crimes to obtain satisfaction" [Encyclopaedia Britannica, 1941]. The name also was used of the evil genius which drives a man to sin and of a man so driven. A Greek word of uncertain origin. The traditional guess is that it is literally "the unforgetting," from a- "not" (see a- (3)) + root of lathein "to forget," aorist of lanthanein "to lie hidden, escape notice," from PIE root *ladh- "to be hidden" (see latent). Or else it might be connected with alaomai "to wander, roam," figuratively "to be distraught." As a proper name, in Greek tradition a son of Neleus and Chloris; brother of Nestor, he was slain by Herakles.
mid-13c., dragoun, a fabulous animal common to the conceptions of many races and peoples, from Old French dragon and directly from Latin draconem (nominative draco) "huge serpent, dragon," from Greek drakon (genitive drakontos) "serpent, giant seafish," apparently from drak-, strong aorist stem of derkesthai "to see clearly," from PIE *derk- "to see" (source also of Sanskrit darsata- "visible;" Old Irish adcondarc "I have seen;" Gothic gatarhjan "characterize;" Old English torht, Old High German zoraht "light, clear;" Albanian dritë "light").
Perhaps the literal sense is "the one with the (deadly) glance." The young are dragonets (c. 1300). Fem. form dragoness is attested from 1630s. Obsolete drake (n.2) "dragon" is an older borrowing of the same word, and a later form in another sense is dragoon. Used in the Bible generally for creatures of great size and fierceness; it translates Hebrew tannin "a great sea-monster," and tan, a desert mammal now believed to be the jackal.