monster; giant monster
Typically refers to a large, destructive, often fictional creature, especially in kaiju films and tokusatsu. Can also be used figuratively for something huge and threatening.
ゴジラは有名な怪獣です。
Godzilla is a famous monster.
怪獣映画が好きです。
I like monster movies.
A giant monster appeared in Tokyo Bay.
The hero fought the giant monster.
The monster rampaged through the city, destroying buildings.
The self-defense forces joined forces to defeat the monster.