San (letter)

San (uppercase/lowercase Ϻ ϻ) was an old letter in the Greek alphabet that was used in some Greek cities before the alphabet got its classical standard form. It looked like the letter Mu (M), but was spoken like S. In the 6th century BC, people stopped using it and wrote Sigma (Σ) instead.

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Greek alphabet
Αα Alpha Νν Nu
Ββ Beta Ξξ Xi
Γγ Gamma Οο Omicron
Δδ Delta Ππ Pi
Εε Epsilon Ρρ Rho
Ζζ Zeta Σσς Sigma
Ηη Eta Ττ Tau
Θθ Theta Υυ Upsilon
Ιι Iota Φφ Phi
Κκ Kappa Χχ Chi
Λλ Lambda Ψψ Psi
Μμ Mu Ωω Omega
Other letters
Ϝϝ Digamma Ⱶⱶ Heta
Ϻϻ San Ϙϙ Koppa
Ϡϡ Sampi Ϛϛ Stigma
Ϸϸ Sho