Hello or Hi ?

Is "hi" more American than British ?
Is it more serious for a teacher to say "Hello" to her pupils ?
Is there any difference between "hi" and "hello" ?
Many thanks.

Yes
Yes
Yes

Don't mention it.

don't mention what ?

Simon was refering to your "many thanks". "Don't mention it" is a frequent reply.

"Hello" is formal, while "hi" is casual. This would depend on the relationship of the teacher with his/her students.

I just looked up ''hi'' in the dictionary and it gave the definition hello.

Still, "hello" isn't as formal as "greetings", "salutations", "good day", "good morning", "god ye good den", etc.

I think that "hello" is one of those words that have no formal or informal connotation. It can be used to greet both your friends at school and guests at a corporate dinner party. Same with "top of the morning to you".

thanks Simon, mjd and A.S.C.M.

Plus you can't answer the phone with hi.

Simon
Good point about the phone. Sometimes I use "Hi". thanks.
Are you an English teacher ?

There was someone once that actually told me that ''hi'' isn't really a word. I don't believe them.

Perhaps they consider 'hi' as an interjection.
To me, it's just like 'hello' so it's a word.
No matter.

They said that you couldn't use that word in Scrabble because it wasn't really a word. I don't believe them.

Did you know that Alexandre Graham Bell (who invented the telephone) considered the correct way to answer a phone to say "Ahoy! Ahoy!"?

There was one person I heard answer the phone with ''what's up''.