vox

Vox, vocis is third declension feminine. As with rex and lex, the x of the nominative is just c plus s, so the stem underneath is voc-, and the whole family follows from it: voco, "call", vocabulum, advoco, invoco, revoco.

It is not only sound. A vox is also a single word considered as a unit of language, which is how grammarians use it and how this corpus uses it constantly: haec vox means "this term". Keep three words apart. Vox is the voice or the isolated word; verbum is the word in a sentence, and in the Vulgate the Word; sermo is connected speech, a conversation or a discourse. English flattens all three into "word" and loses the distinction. Idiom: magna voce, "loudly", with the manner in the ablative. English voice, vocal, vowel, vocation, provoke, advocate; French voix, Spanish voz.