-τερος

From Proto-Indo-European *-teros.

-τερος • (-teros) m (feminine -τέρᾱ, neuter -τερον); first/second declension

1. Used on adjectives that express some notion of contrast with an antonym

   ‎ἡμεῖς (hēmeîs, “we”) + ‎-τερος (-teros) → ‎ἡμέτερος (hēméteros, “our”)

2. Added to adjective stems to form comparative forms

   ‎δῆλος (dêlos, “clear”) + ‎-τερος (-teros) → ‎δηλότερος (dēlóteros, “clearer”)

   ‎σοφός (sophós, “wise”) + ‎-τερος (-teros) → ‎σοφώτερος (sophṓteros, “wiser”)

• -ίων (-íōn), -ων (-ōn)

• Smyth, Herbert Weir (1920) “Part II: Inflection”, in A Greek grammar for colleges, Cambridge: American Book Company, § 313

-τερος • (-teros)

1. The ancient suffix which has formed absolute comparative adjectives; in Modern Greek they are reanalysed.

   See the modern suffixes for regular comparative adjectives: -ότερος (-óteros), -ύτερος (-ýteros), -έστερος (-ésteros)^[1]

• Note, that irregular comparative adjectives like κατώτερος (katóteros) were already formed in Ancient Greek; from adverb κάτω (kátō, “down”) + -τερος (-teros)
• The ancient differentiation of -ότερος / -ώτερος became -ότερος (-óteros) in Modern Greek.
• The -τερος (-teros) ending is a useful mnemonic aid to form Modern Greek absolute comparatives by adding it to the neuter nominative singular form of the regular positive adjectives.^[2]

• -τερός (-terós)
• -ότατος (-ótatos) (a suffix for superlative adjectives)