-ιος

From Proto-Indo-European *-yós.

-ῐος • (-ios) m (feminine -ῐ́ᾱ, neuter -ῐον); first/second declension

1. Suffix added to nouns or adjectives, forming adjectives: pertaining to, belonging to ("of").

• Greek: -ιος (-ios)

• Smyth, Herbert Weir (1920) “Part III: Formation of Words”, in A Greek grammar for colleges, Cambridge: American Book Company, § 858.2

From Ancient Greek -ῐος (-ios). Found in inherited words, and compositions of formal words.

for older or formal words:

• IPA^(key): /i.os/
• Hyphenation: ι‧ος

-ιος • (-ios) m (feminine -ια, neuter -ιο)

1. Used to form nouns and adjectives indicating origin:

   ‎Κύπρος (Kýpros, “Cyprus”) + ‎-ιος (-ios) → ‎Κύπριος (Kýprios, “Cypriot”) (noun, demonym)

   Related term: -αίος (-aíos) for demonyms

   ‎θάλασσα (thálassa, “sea”) + ‎-ιος (-ios) → ‎θαλάσσιος (thalássios, “marine”) (adjective)

   ‎αιώνας (aiónas, “century”) + ‎-ιος (-ios) → ‎αιώνιος (aiónios, “eternal”) (adjective)

Modern formations of derivatives from verbs or adjectives + -ιος (-ios)

in one syllable:

• IPA^(key): /i̯os/ with palatal variants /ʝos, ʎos, ços, ɲos/ depending on the preceding consonant
• Hyphenation: ιος

-ιος • (-ios) m (feminine -ια, neuter -ιο)

1. Used to form adjectives indicating property, characteristic of the prototype word:

   ‎σαπίζω (sapízo, “I rot”) + ‎-ιος (-ios) → ‎σάπιος (sápios, “rotten”) /ˈsapços/ (from verb)

   ‎καθαρός (katharós, “clean”) + ‎-ιος (-ios) → ‎καθάριος (kathários, “clear”) /kaˈθaɾʝos/ (from adjective)

• -ειος (-eios)

• -ιός (-iós)

• "-ιος" - Λεξικό της κοινής νεοελληνικής [Dictionary of Standard Modern Greek], 1998, by the "Triantafyllidis" Foundation.