1175-1225; (v.) Middle Englishslumeren, frequentative of slumen to doze, derivative of Old Englishslūma sleep (see -er6); compare Germanschlummern; (noun) Middle Englishslomur, slomber, derivative of the v.
mid-14c., alteration of slumeren (early 13c.), frequentative form of slumen "to doze," probably from O.E. sluma "light sleep" (cf. M.Du. slumen, Du. sluimeren, Ger. schlummern "to slumber"). Frequentative on the notion of "intermittent light sleep." The noun is attested from late 14c. Slumber party first recorded 1942.