Sou \Sou\, n.; pl. {Sous}or. [F. sou, OF. sol, from L. solidus a gold coin, in LL., a coin of less value. See {Sold}, n., {Solid}, and and cf. {Sol}, {Soldo}.] An old French copper coin, equivalent in value to, and now displaced by, the five-centime piece (1/20 of a franc), which is popularly called a sou. [1913 Webster]