From Wiktionary, the free dictionary
ς • (s ) (lowercase , uppercase Σ )
The lower case letter sigma of the Ancient Greek alphabet when used as the final letter in a word (a final sigma ). In all other positions in a word the normal sigma (σ ( s ) ) is used.
( Greek-script letters) Α α , Β β , Γ γ , Δ δ , Ε ε , Ζ ζ , Η η , Θ θ , Ι ι , Κ κ , Λ λ , Μ μ , Ν ν , Ξ ξ , Ο ο , Π π , Ρ ρ , Σ σ ς , Τ τ , Υ υ , Φ φ , Χ χ , Ψ ψ , Ω ω
( non-Classical letters ) Ϝ ϝ , Ͷ ͷ , Ͱ ͱ , Ϻ ϻ , Ϙ ϙ , Ͳ ͳ
( punctuation ) · ;
( diacritics ) ᾿ ῾ ◌́ ◌̀ ῀ ¨
ς • (s ) (lowercase , uppercase Σ )
The lower case letter sigma (σίγμα τελικό ( sígma telikó ) ) of the Greek alphabet when used as the final letter in a word (a final sigma ). In all other positions in a word the normal sigma (σ ( s ) ) must be used.