Mustache is the US spelling, while moustache is the preferred spelling for English speakers outside of the USA.
There are two accepted spellings, with or without the "O" : mustache/moustache. (The growth of hair between the nose and mouth.)
In Britain, it is spelled moustache. In the US, it is spelled mustache.
The term may be spelled mustache or moustache(facial hair typically between the nose and upper lip).
It is "moustache"
Moustache
A moustache can be trimmed or waxed .
The French word moustache is a cognate and means mustache.
From the moustache shop
He has a "handlebar" moustache.
whiskers
Yes he has a handle bar moustache.
The usual spelling is "mustache" but also "moustache."