From Latin 'invocare' (to call upon), from PIE *wekw- (to speak) — same root as 'voice,' 'vocal,' and 'provoke.'
To call on a deity, spirit, or authority for aid, inspiration, or protection; to cite as an authority or justification; to put into effect.
From Latin invocāre ("to call upon, appeal to, summon"), a compound of in- ("upon, into") and vocāre ("to call"), from vōx (genitive vōcis, "voice, sound, word"). Vōx derives from PIE *wekʷ- ("to speak, say"), one of the core roots for vocal communication in Indo-European, yielding: Greek ἔπος (épos, "word, epic verse") and ὄψ (óps, "voice"), Sanskrit vāk- ("speech, voice" — personified as the goddess Vāc), Old English wōma ("noise, tumult"), and possibly English voice itself (though voice entered via Old French from Latin). The prefix in- gives invocāre a directional force: to call upon a higher power, to summon authority
Nearly every epic poem in Western literature begins with an invocation. Homer's Iliad opens with 'Sing, O goddess, the anger of Achilles,' and the Odyssey with 'Tell me, O Muse, of that ingenious hero.' Virgil, Dante, and Milton all followed this convention. The invocation was not merely decorative — it was a genuine appeal for divine inspiration, reflecting the belief that poetry