-tio

• -siō (in primarily third conjugation verbs with stems ending in -t-, -d-, -rg-, -ll-, or -rr-.)
• -ciō (Medieval Latin)

Probably from Proto-Italic *-tjō, an n-stem extension of Proto-Indo-European *-tis.

Alternatively, from Proto-Indo-European *-Hō or from Proto-Indo-European *-tyon with Old Armenian -ութիւն (-utʻiwn) as a cognate. (Can this⁽⁺⁾ etymology be sourced?)

• (Classical Latin) IPA^(key): [ti.oː]
• (modern Italianate Ecclesiastical) IPA^(key): [t̪͡s̪i.o] (stressed on the antepenult)

-tiō f (genitive -tiōnis); third declension

1. -tion, -ation, -ing; suffixed to verbs to form action nouns denoting a process, action, or result of an action.

   dictātiō (“a dictating, dictation”) ← dictō, dictātum (“to dictate”)

   quadripartītiō (“a division into four parts”) ← quadripartiō, quadripartītum (“to divide into four parts”)

This suffix is one of many (including -tus, -tor, -tiō, -tim, -tō, -tūra) that all use the same verb stem as the supine, perfect passive participle, and/or future active participle, found in the verb's fourth principal part. This stem is conventionally considered to end in -t- (or for some verbs, -s-), which would imply analyzing the suffixes as -us, -or, -io, -im, etc. However, from an etymological perspective it is more accurate to identify -t-/-s- as the initial consonant of these suffixes.

• Most 1st conjugation verbs attach -t- after the theme vowel -ā-: e.g. amō, amātor, but a few form this principal part differently: e.g. secō > sectiō. Similarly, many 4th conjugation verbs use -ī-t-, but some use other formations, e.g. saliō > salto.
• 2nd conjugation verbs are less consistent. Many use -i-t- (moneō, monitor); some attach -t- after the final consonant of the root (doceō > doctor); a considerable number lack this principal part. Monosyllabic stems use -ē-t-: ex-pleō (stem plē-) > explētiō.
• Many 3rd conjugation verbs (and some 1st, 2nd and 4th) attach -t- directly after a consonant, which can cause complex changes. When -t- is placed after -t- or -d-, the consonants merge to -ss- (simplified to -s- if not preceded by short vowel): metō > messor, caedo > caesūra. Occasionally -s- is used after other consonants: curro > cursim, mergo > mersō. Before -t-, -b- -g- are regularly devoiced to -p- -c-: scrībō > scrīptor; frīgō > frīctus. The addition of -t- can be accompanied by various other changes, including vowel shortening, vowel lengthening, consonant insertion, or consonant deletion; see -tus for more information.

The suffix is occasionally added to other parts of speech, or appears in situations where no related verb apparently exists; more at -ātiō.

gradātiō (“making of a staircase or steps”), from gradus (“step, pace”).

Third-declension noun.

• -tūra, -tus

• -ātiō
• -itiō
• -ītiō

• Haudry, Jean (1981), L'indo-européen, pages 55-56
• Sihler, Andrew L. (1995), New Comparative Grammar of Greek and Latin, Oxford, New York: Oxford University Press, →ISBN