top hat

[georgeg]

what is the little chinese looking hat that appears over some letters in some words called?

[twopennorth]

It's the circumflex accent

[Peter Pedant]

I think it is always called a circumflex accent - some accents vary according to the language.

In French words it is silent and just represents an 's' which has dropped out along the way. French fenetre comes from fenestra (L)

In Vietnamese it's a tone