-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): /t͡si.o/, (stressed on the antepenult)

-tiō f (genitive -tiōnis); third declension

1. -tion, -ation, -ing; suffixed to a verb (usually a participle form) to form a noun relating to some action or the result of an action.

   dictātiō (“a dictating, dictation”), from dictātum, supine of dictō (“I dictate”)

   quadripartītiō (“a division into four parts”), from quadripartītum, supine of quadripartiō (“I divide in four parts”)

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