Green’s Dictionary of Slang

a moustache.

1967		C. Drummond Death at Furlong Post 181: Take my oath it’s he [...] with his hair parted..and the mush shaved off his lip [OED].
2002		‘dravidian brahmin’ posting 7 Aug. at Forumhub.com 🌐 As we all know from tamil films, bravery, virility and potency are directly proportional to the size of a man’s moustache [...] many of the 97.5% of brahmins that you so kindly mentioned do not sport a moosh. Therefore they are impotent.
2003		R. Guy ‘Musiri Subramania Iyer’ at Sangeetham.com 🌐 Tukaram has a moustache and as Musiri was a clean-shaving Brahmin a ‘mush’ was attached to his upper lip.