* somnolence: sleepiness, drowsiness
* insomnia: inability to sleep
* somnambulism: sleepwalking
* hypnotic: inducing sleep
* somniferous: causing sleep
There are also some other related roots:
* dorm-: meaning "sleep" or "to sleep"
* sopor-: meaning "sleep" or "lethargy"
While these roots are not as common as "somn-", they can be found in words like:
* dormant: inactive, as if asleep
* dormouse: a small, furry animal that hibernates in the winter
* soporific: causing sleep
* sopor: a state of deep sleep or unconsciousness