What's the difference between "skeptical" and "sceptical" exactly?
and which is the British usage? Thank you.

Question

What's the difference between "skeptical" and "sceptical" exactly?
and which is the British usage? Thank you.

Answer

I think British is sceptical, and skeptical is US. But don't get hung up on spelling. Life's too short.

Answer

Skeptical is British.
Sceptical is no longer in common use and was originally the US spelling of the word. 
Both mean the same thing: doubtful, inclined to mistrust
A word with a similar meaning you might want to look up is cynical. This other word has a more negative connotation compared to skeptical.

Answer

Australians use sceptical

Answer

skeptical is the American spelling of sceptical

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brits got the spelling wrong? :P