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