What type of word is 'hello'?

is the work "hello" a verb noun adjective or pronoun or whatever

just for curiousity I was wonderin

It depends on how you use it.

noun 4. the call “hello” (used as an expression of greeting): She gave me a warm hello.
–verb (used without object) 5. to say “hello”; to cry or shout: I helloed, but no one answered.
–verb (used with object) 6. to say “hello” to (someone): We helloed each other as though nothing had happened.

or it could also be an iterjection...

"Hello! What is this I have in my eye?" (said with a British accent =P )

If you go to dictionary.com, you'll see that it's mostly used as a noun and or an interjection.

thanks