The word hilarious means very funny and here are a few sentences

• That was a hilarious joke!!

• He is the most hilarious kid in the class

• OMG, she looks hilarious!

My kids think Will Ferrell's new movie is just hilarious.

Chris Rock is a hilarious stand up comedian.

No, but it is an adjective. This is because hilarious describes a noun; That is hilarious. or The hilarious T-shirt got a lot of attention.

The reason it isn't a verb is because it describes the noun, but it does not tell what the noun is doing. Hilarious cannot be a verb because there is no way to do the action of hilarious; you can't hilarious a nice hat or hilarious to the store; it isn't possible. However, you can describe another adjective with it by adding -ly:

The hilariously green bubble reflected the lake behind it.

No. You can do something hilariously (adverb) and something can be hilarious (adjective). I am Hilarious. (adjective, describes what I am). I hilarious. (invalid way to use it).