IPA: /fərˈbɪdə/
KK: /fərˈbɪdər/
A person who prohibits or disallows something.
The forbidder of the event made sure no one could enter without permission.
Forbidder → It is formed from "for-" (meaning against) and "bid" (from Old English "biddan", meaning to ask or command) with the suffix "-er" (meaning a person who). The word "forbidder" refers to a person who commands against something or prohibits it.
Think of someone who is 'against' ('for-') what is being 'commanded' ('bid') — that's why a forbidder is someone who prohibits or commands against something.