Institutio Oratoria

For instance Marcus Caelius wishes to prove that he is homo frugi, not because he is abstemious (for he could not even pretend to be that), but because he is useful to many, that is fructuosus, from which frugalitas is derived. Consequently we find room for etymology when we are concerned with definitions.

Sometimes again this science attempts to distinguish between correct forms and barbarisms, as for instance when we are discussing whether we should call Sicily Triquetra or Triquedra, or say meridies or medidies, not to mention other words which depend on current usage.