As nouns the difference between san and sai
is that
san is a letter of the Archaic Greek alphabet (uppercase Ϻ, lowercase ϻ) that came after pi and before qoppa while
sai is a handheld weapon with three prongs, used in some Oriental martial arts.
As a proper noun San
is a member of the ethnically distinct, short-statured nomadic people of southern Africa.
As an acronym SAN
is styrene-acrylonitrile resin.