Green’s Dictionary of Slang

1. a woman [play on cat n.¹ (1c)].

1812

Spirit of Irish Wit 260: Kept the old mouser in a fry. / Until they got to Oswestry.

2. the vagina.

1890–1904

Farmer & Henley Sl. and Its Analogues.

3. a cat o’-nine tails [play on cat n.³ ].

1890–1904

Farmer & Henley Sl. and Its Analogues.

4. a detective [SE mouser, a cat].

1860		John Horsleydown 266: Two shrewd ‘mousers’, were sent off at once with Mr. Gee to York Street .
1949		Monteleone Criminal Sl. (rev. edn).

5. a black eye.

1901		Bateman & LeBrunn [perf. Marie Lloyd] Folkestone for the Day 🎵 The landlord got two ‘mousers’ and the deuce there was to pay.
1965–70		in DARE.

6. (US) a homosexual.

1914		Jackson & Hellyer Vocab. Criminal Sl. 60: mouser [...] Current in cosmopolitan circles. A ‘fairy;’ a character obsessed by lewd passions.
1931		Irwin Amer. Tramp and Und. Sl. 201: While there are grossly obscene verses [...] the men and boys who persist in singing or reciting this muck are regarded as ‘mousers’ or ‘fluters’ and as such avoided.
1941		G. Legman ‘Lang. of Homosexuality’ Appendix VII in Henry Sex Variants.
1949		Monteleone Criminal Sl. (rev. edn).
1965		Guild Dict. Homosexual Terms 31: mouser (n.): A homosexual; probably from the verb which meant to hunt or search industriously, or to move about softly in search of something, and even to prowl (ca. 1575). (Slang.) It has been recorded that pedicants have been known to have tattooed a mouse crawling between their buttocks.

7. (orig. US, also mousie) a moustache [supposed resemblance].

1931		D. Runyon ‘Breach of Promise’ in Runyon on Broadway (1954) 18: He is a little guy [...] with a bald head, and a small mouser on his upper lip.
1944		E. Wilson 27 June [synd. col.] About the mouser — Dewey sprouted it in ’25 when he was bicycling through France.
1959		J. Yates-Benyon Weak and the Wicked 601: ‘Yes, that disgusting moustache,’ I was callously brutal. ‘Shave it off’ [...] ‘Ask of me anything else you will, but the old mousie stays.’.
1998		I. Welsh Filth 26: Lennox has trimmed his mouser.
2023		R. Milward Man-Eating Typewriter 6: ‘A little handlebar mouser’.