Augustine, De Doctrina Christiana:
Duabus autem causis non intelleguntur quae scripta sunt, si aut ignotis aut ambiguis signis obteguntur. Sunt autem signa vel propria vel translata. Propria dicuntur, cum his rebus significandis adhibentur propter quas sunt instituta, sicut dicimus bovem, cum intellegimus pecus quod omnes nobiscum latinae linguae homines hoc nomine vocant. Translata sunt, cum et ipsae res quas propriis verbis significamus, ad aliquid aliud significandum usurpantur, sicut dicimus bovem et per has duas syllabas intellegimus pecus quod isto nomine appellari solet, sed rursus per illud pecus intellegimus evangelistam, quem significavit scriptura interpretante apostolo dicens: Bovem triturantem non infrenabis.
But for two causes are things which have been written not understood: if they are hidden by signs which are either unknown or ambiguous.
Now signs are either literal (propria) or metaphorical (translata = Gk. μεταφορικά).
They are called literal when they are furnished for the signification of the things because of which they were originally established, as when we say “ox” (bovem) when we understand the herd-animal (pecus) which all men of the Latin tongue with us call by this noun.
They are metaphorical, when even the very things which we signify by their literal words are used to signify something else, as when we say “ox” (bovem) and by these two syllables we understand the herd-animal (pecus) which is usually named by that noun, but again we understand through the herd-animal the evangelist, which scripture signifies when it says with the Apostle as translator: Thou shalt not muzzle the ox that treadeth out the corn. [1 Tim. 5.18]
Thanks, dear reader, should you ever find me, for sharing my curiosity about words.