- somnolence (n.)
- late 14c., from Old French sompnolence, from Latin somnolentia "sleepiness," from somnolentus, from somnus "sleep," from PIE *swep-no, from root *swep- "sleep" (cf. Sanskrit svapnah, Avestan kvafna-, Greek hypnos, Lithuanian sapnas, Old Church Slavonic sunu, Old Irish suan, Welsh hun "sleep," Latin sopor "a deep sleep," Old English swefn, Old Norse svefn "a dream").