Lewis & Short

somnŭlentus (somnŏl-), a, um, adj. [somnus], full of sleep, i. e. sleepy, drowsy, dozy, somnolent (post-Aug.), App. M. 1 fin.; 10, p. 251, 37.
Hence, adv.: somnŏlen-ter, sleepily, Hier. in Psa. 118; Sol. 20, 7.