Etymologiae, Book I, chapters 30-32: De glossis to De barbarismo
Chapter XXX. On glosses The gloss takes its name from the Greek interpretation of the tongue. The philosophers call it the “adverb,” because it designates by one single word the word whose meaning is sought. For it declares what that thing is, set down in one word, as: conticescere is “to be silent.” Likewise: “He drinks his open side”; haurit means “strikes.” Likewise when we say terminus, “end,” or interpret populatas as “laid waste,” and in general when we make plain the sense of one word by one word.
Chapter XXXI. On differences Difference is a species of definition, which the writers of the arts call that of the same and of the other. For these two, confused by a certain common ground between them, are separated by the difference added, through which each is known; as when it is asked what lies between a king and a tyrant, the difference being added, what each is is defined: the king is modest and temperate, the tyrant cruel. For when the difference between these two has been set down, what each is is known. So also with the rest.
Chapter XXXII. On barbarism A barbarism is a word uttered with a corrupted letter or sound. By letter, as floriet, when one ought to say florebit; by sound, if the first syllable is lengthened in place of the middle one, as latebrae, tenebrae. It is called barbarism from the barbarian nations, since they did not know the purity of Latin speech. For each nation, together with its wealth, sent to Rome the faults both of speech and of manners. Between barbarism and barbarolexis there is this difference, that barbarism occurs in a Latin word when it is corrupted; but when barbarous words are brought into Latin speech, it is called barbarolexis. Likewise, when the fault of speech occurs in prose it is called barbarism; when in metre, it is called metaplasm. Barbarism occurs in writing and in pronunciation. In writing in four ways: if someone in a word adds, changes, transposes or removes a letter or syllable. In pronunciation it occurs in times, tones, aspirations and the rest that follow. Through times, barbarism occurs if a short syllable is put for a long one, or a long for a short. Through tones, if the accent is shifted to another syllable. Through aspiration, if the letter H is added where it ought not to be, or taken away where it ought to be. Through hiatus, whenever in pronunciation the verse is split before it is completed, or whenever a vowel follows a vowel, as Musae Aonides. Barbarism is made also by motacismus, iotacismus and labdacismus.
Motacismus is when a vowel follows the letter M, as bonum aurum, iustum amicum; but this fault we avoid either by suspending the letter M or by dropping it. Iotacismus is when the sound of the letter iota is doubled, as Troia, Maia; where the pronunciation of these letters will be so slight that one iota, not two, seems to sound. Labdacismus is if two L’s are pronounced for one, as the Africans do, as colloquium for conloquium; or whenever we utter one L too thinly, two too broadly. The contrary is right; for we ought to utter one more broadly, two more thinly. Collisio is whenever the end of the last syllable is at the beginning of another, as matertera.