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 especially past participles
( allusion; creation; fusion; notion; torsion ).
Origin:
< Latin -iōn- (stem of -iō) suffix forming nouns, especially on past participle stems; replacing Middle English -ioun < Anglo-French < Latin -iōn-