IPA: /ˈkɔːzər/
KK: /ˈkɔːzər/
A person or thing that makes something happen or brings about a result.
The storm was the main causer of the flooding in the area.
Causer → The word is formed from "cause" (from Old French *cause*, meaning reason or motive) and "-er" (meaning a person who). A causer is a person who causes something to happen or brings about an event.
Think of someone who is the 'reason' ('cause') for something happening — the '-er' indicates that this person is the one who causes it.