מ ‘Mem’ — the thirteenth letter of the Hebrew alphabet. The origin of its name is supposed to be מַיִם (= water); so called in allusion to the ancient form of this letter resembling waves of water. מ alternates with the other labials, esp. בּ, פּ and נ. It has a final form: ם. In PBH it has the numerical value of forty (מ) and six hundred (ם).