Someone or something that causes fear is intimidating. Bullies are intimidating.
Anyone or anything that is fearsome, daunting, or terrifying could be called intimidating. Looking at a huge list of vocabulary words is intimidating. Any difficult job can be intimidating. Lots of people find public speaking intimidating. Climbing into the mouth of a volcano and trying to take a photograph for National Geographic would be extremely intimidating, because you could die, and if you don't, what if your pictures aren't that good?