\'män-stər\ n 1 : an abnormally developed
plant or animal. 2 : an animal of strange or
terrifying shape; also : one unusually large of its kind. 3 : an extremely ugly, wicked, or
cruel person.
Example:
To usually mean make-believe and often magical creatures of unknown or known origin, like
Slenderman or
Bigfoot. When used to describe a person, however, it's much more
demeaning. You're basically denying that person of having any resemblance of a human being - morals, emotions etc. It's not a nice thing. Some people are cold, but not all to their very core like some seem.
My own grandmother called me a monster. She was probably right, but it still hurt...