stache
Word family
Synonym discussion
Sense: noun/1
'Stache' is the playful, highly informal short form. Friends might say it when joking about someone's look, a costume, or a barber visit. 'Moustache' is the full standard word and is the safer choice in careful writing; 'mustache' is the same word in the usual American spelling. 'Beard' is broader and covers hair on the cheeks and chin, so it cannot replace 'stache' when you mean hair only above the upper lip. 'Goatee' is even narrower: it refers to a pointed beard on the chin, sometimes with a moustache but not necessarily. If you are writing formally, choose 'moustache' or 'mustache'; if you are teasing a friend about a new look, 'stache' sounds natural.
Etymology
'Stache' is a clipped informal form of 'moustache'. The older word came into English through French 'moustache' and ultimately goes back to Greek 'mystax', meaning the upper lip or the hair on it. English speakers later shortened the word in casual speech to make it quicker and more playful.