-ion

a suffix, appearing in words of Latin origin, denoting action or condition, used in Latin and in English to form nouns from stems of Latin adjectives (communion; union), verbs (legion; opinion), and esp. past participles (allusion; creation; fusion; notion; torsion).

Also, -ation, -ition, -tion. Cf. -cion, -xion.

[ < L -ion- (s. of -io) suffix forming nouns, esp. on ptp. stems; r. ME -ioun < AF < L -ion-]

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