IPA: /ˈslʌmbərər/
KK: /ˈslʌmbərər/
A person who is sleeping or in a state of rest.
The slumberer lay peacefully on the couch, unaware of the noise around them.
Slumberer → It is formed from "slumber" (from Old English *slumrian*, meaning to sleep) and "-er" (meaning a person who). A slumberer is a person who is sleeping or in a state of slumber.
Think of someone who is in a state of sleep ('slumber') — the '-er' just means a person. A slumberer is someone who is sleeping.