IPA: /ˈslɒbərə/
KK: /ˈslɑːbərər/
A person who drools or lets saliva run from their mouth, often in a messy way.
The dog was a slobberer, leaving wet spots on the floor after drinking water.
Slobberer is formed from "slobber" (from Middle English *slobberen*, meaning to let saliva drip) and the suffix "-er" (meaning a person who). A slobberer is a person who slobbers or lets saliva drip.
Think of someone who 'lets saliva drip' — that's what a slobberer does, and the '-er' just means a person.