What is the meaning of -ioun?

Forms nouns from French or Latin roots; -ion.

Sandved, Arthur (1985), “9. Derivational Suffixes”, in Introduction to Chaucerian English (Chaucer Studies; 11), Part II: Morphology, Cambridge: D. S. Brewer, →ISBN, →OCLC, page 41.

-iǒun, suf.”, in MED Online, Ann Arbor, Mich.: University of Michigan, 2007.

alternative form of -ien (-ian)

Source: wiktionary.org