Herbert Weir Smyth, A Greek Grammar for Colleges

FORMATION OF CASES: NOMINATIVE SINGULAR

a. A labial (π, β, φ) + ς becomes ψ (97).

b. A dental (τ, δ, θ) + ς becomes σς (98), which is reduced to ς (107).

c. A palatal (κ, γ, χ) or κτ ¨ ς becomes ξ (97).

(The same changes occur in the dative plural.)

γύ_ψ vulture γυ_π-ός, Ἄραψ Arab Ἄραβ-ος; κακότης baseness κακότητ-ος, ἐλπίς hope ἐλπίδ-ος, ὄρνι_ς bird ὄρνι_θ-ος; φύλαξ guard φύλακ-ος, μάστι^ξ scourge μάστι_γ-ος, σάλπιγξ trumpet σάλπιγγ-ος, ὄνυξ nail ὄνυχ-ος, νύξ night νυκτ-ός; ἅλ-ς salt ἁλ-ός, ἰχθύ_ς fish ἰχθύ-ος; ἐλέφα_ς elephant ἐλέφαντ-ος.

[*] 242. Masculine and feminine stems ending in ν, ρ, and ς reject ς and lengthen a preceding vowel if short (ε to η, ο to ω).

δαίμων divinity δαίμον-ος, χειμών winter χειμῶν-ος, λιμήν harbour λιμέν-ος, Ἕλλην Greek Ἕλλην-ος; ῥήτωρ orator ῥήτορ-ος, ἀήρ air ἀέρ-ος, φώρ thief φωρ-ός, τριήρης trireme (stem τριηρεσ-, 263 b), αἰδώς shame (stem αἰδοσ-, 266). On μήν see 259 end. For stems in ες, nominative -ος, see 263 c.

[*] 243. Masculine stems in οντ drop τ (133) and lengthen ο to ω: γέρων old man γέροντ-ος, λέων lion λέοντ-ος.

[*] 243 D. Hdt. has ὀδών tooth ὀδόντ-ος. Attic ὀδούς has the inflection of a participle in -ους (307).

[*] 244. Neuters show the pure stem, from which final τ and other consonants not standing at the end of a word (133) are dropped: ἅρμα chariot ἅρματ-ος, πρᾶγμα thing πρά_γματ-ος, γάλα milk γάλακτ-ος (133 b).

[*] 245. Summary.—ς is added to stems ending in a labial, dental, palatal, and in αντ, εντ, υντ; to some stems in ν (as εἷς one ἑν-ός, μέλα_ς black μέλαν-ος); to stems in ευ, αυ, ου; and to masc. and fem. stems in ι and υ. ς is not added to most stems ending in ν, nor to those in οντ, ρ, ες, ας, ος, υ (neut.), ω（ϝ), ο（ι).