-ια

From Proto-Indo-European *-ih₂ ~ *-yéh₂s, related to -ίᾱ (-íā) (from Proto-Indo-European *-i-eh₂). Cognate with Latin -ia. In some contexts, (e.g. in words like ἀλήθεια (alḗtheia) and πᾰρᾰ́νοιᾰ (paránoia)) the use of this suffix may have been an innovative replacement of earlier formations in -ίᾱ (-íā) (which was kept or changed to -ίη (-íē) in some dialects).^[1][2]

After a consonant, the vowel *i changed to a semivowel *y and triggered palatalization in Proto-Greek, resulting in many nouns and adjectives ending in -σσᾰ (-ssa), -ττᾰ (-tta), -ζᾰ (-za). It also undergoes metathesis, resulting in -ιρᾰ (-ira), and -ινᾰ (-ina).

-ῐᾰ • (-ia) f (genitive -ῐ́ᾱς); first declension

1. Primitive suffix added to the stems of adjectives in -ύς (-ús) and some nouns to form feminine gender

   ‎ἡδῠ́ς (hēdús, “sweet”, masculine) + ‎-ῐᾰ (-ia) → ‎ἡδεῖᾰ (hēdeîa, feminine)

   ‎ἱερεύς (hiereús, “priest”, masculine) + ‎-ῐᾰ (-ia) → ‎ἱέρειᾰ (hiéreia, feminine)

2. Suffix added to the stems of adjectives in -ής (-ḗs) to form abstract nouns

   ‎ᾰ̓ληθής (alēthḗs, “true”) + ‎-ῐᾰ (-ia) → ‎ᾰ̓λήθειᾰ (alḗtheia, “truth”)

Nouns formed with the suffix always have recessive accent.

• -εια (-eia)
• -ινα (-ina)
• -μετρία (-metría)

• Smyth, Herbert Weir (1920) “Part III: Formation of Words”, in A Greek grammar for colleges, Cambridge: American Book Company, § 859.6