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."
"to call; to name" (archaic), from Old English cleopian, clipian "to speak, call; summon, invoke; implore," which is of uncertain origin.
late 13c., "command on oath;" c. 1300, "summon by a sacred name, invoke by incantation or magic," from Old French conjurer "invoke, conjure" (12c.) and directly from Latin coniurare "to swear together; conspire," from assimilated form of com "with, together" (see con-) + iurare "to swear," from ius (genitive iuris) "law, an oath" (see jurist).
The magical sense is from the notion of "constraining by spell" a demon to do one's bidding. Related: Conjured; conjuring. Phrase conjure up "cause to appear in the mind" (as if by magic) attested from 1580s.
c. 1500, from French implorer and directly from Latin implorare "call on for help, beseech, beg earnestly," with a literal sense probably of "plead tearfully, invoke with weeping," from assimilated form of in- "on, upon" (from PIE root *en "in") + plorare "to weep, cry out," a word of unknown origin. Related: Implored; imploring; imploringly; imploration.
mid-15c., "a curse, cursing," from Latin imprecationem (nominative imprecatio) "an invoking of evil," noun of action from past participle stem of imprecari "invoke, pray, call down upon," from assimilated form of in- "into, in, within" (from PIE root *en "in") + precari "to pray, ask, beg, request" (from PIE root *prek- "to ask, entreat"). "Current limited sense is characteristic of human nature" [Weekley].