somn(i)-

Sleep.

Latin somnus, sleep.

A somnambulist is a sleepwalker (Latin ambulare, to walk), for which the associated noun is somnambulism; in medicine, a somnifacient is a drug that induces sleep or drowsiness; something somniferous tends to induce sleep; somnolent can refer to a person who is sleepy or drowsy or to something inducing drowsiness.