Today's Quintilian: 8.6.1-3

[6] I. Tropos est verbi vel sermonis a propria significatione in aliam cum virtute mutatio. Circa quem inexplicabilis et grammaticis inter ipsos et philosophis pugna est quae sint genera, quae species, qui numerus, quis cuique subiciatur. II. Nos, omissis quae nihil ad instruendum oratorem pertinent cavillationibus, necessarios maxime atque in usum receptos exsequemur, haec modo in his adnotasse contenti, quosdam gratia significationis, quosdam decoris adsumi, et esse alios in verbis propriis, alios in tralatis, vertique formas non verborum modo sed et sensuum et compositionis. III. Quare mihi videntur errasse qui non alios crediderunt tropos quam in quibus verbum pro verbo poneretur. Neque illud ignoro, in isdem fere qui significandi gratia adhibentur esse et ornatum, sed non idem accidet contra, eruntque quidam tantum ad speciem accommodati.

1. A trope is the conversion of a word or phrase, from its proper signification to another, in order to increase its force. Concerning tropes grammarians have carried on interminable disputes among themselves and with the philosophers; disputes as to what genera there are of them, what species, what number, and which are subordinate to others. 2. For myself omitting all such subtilties as useless to form an orator, I shall speak only of those tropes which are most important and most in use; and in regard to these, too, I shall content myself with observing, that some are adopted for the purpose of adding to significance, others for the sake of ornament; that some take place in words used properly, and others in words used metaphorically; and that tropes occur, not only in single words, but also in thoughts, and in the structure of composition. 3. Those, therefore, appear to me to have been in error, who thought that there were no tropes but when one word is put for another; nor am I insensible, that in the tropes which are used with a view to significance, there is also embellishment; but the reverse is not the case, as, there are some that are intended for embellishment only.