friend, n. — Green’s Dictionary of Slang

friend n.

1. a prostitute’s boyfriend or lover, but not necessarily her pimp.

1821		‘An Amateur’ Real Life in London I 214: The term friend, is in constant use among accessible ladies, and signifies their protector or keeper.
1833		‘The Beak and Trap to Roost are Gone’ in Swell!!! or, Slap-Up Chaunter 48: All’s gloom where’er we bend; Your glim except, that shows some frow / Has just brought home a friend.
1842		Whip & Satirist of NY & Brooklyn (NY) 3 Dec. n.p.: Her establishment is ther ‘crack’ of the city for boarding ladies amnd their ‘friends’.
1966		Trimble 5000 Adult Sex Words and Phrases.

2. (US black) menstruation; thus euph. phr. I have friends to stay, I am menstruating.

1949		Monteleone Criminal Sl. (rev. edn) 91: friends to stay A female menstruation period. [Ibid.] 114: have a friend To menstruate.
1967–8		Baker et al. CUSS 121: Friend, get your [...] Friend, have a visit from a Be menstruating.
1972		(con. 1950s) Jacobs & Casey Grease II iv: Your friend. Your period.

In phrases

my friend (n.) (also my little friend, my others)

menstruation.

1890-1904		Farmer & Henley Sl. & Its Analogues III 73/2: Friend (or Little Friend) [...] The menstrual flux [...] whose appearance is sometimes announced by the formula ‘My little friend has come’.
1948		Word 4 183: List of Expressions [for menstruation] [...] My friend is here [...] The girl friend, to have the girl friend. [In spoken use among women.].
1974		J. Lahr Hot to Trot 94: ‘Take your pants off, darling.’ ‘I’ve got “my friend”.’.
1982		N. Keesing Lily on the Dustbin 32: There are probanbly as many slang synonyms for menstruation and its appurtenances as there are offices and factories and girls’ schools in Australia [...] Older generations talk of ‘my friend’ or ‘the curse’.
1982		A. Walker Color Purple 161: Just when I think I’ve learned to live with the heat, the constant dampness, [...] my friend comes.
1988		R. Doyle Commitments 159: Me others were late.
1996		(con. 1970) G. Moxley Danti-Dan in McGuinness Dazzling Dark (1996) I iv: I’m due my Auntie Jane. My friend, do you get me?
1999		J. Randall ‘A Visit from Aunt Rose’ in Verbatim XXV:1 Winter 25: The personification of the period, odd as it may be, is a popular coding. Generally the period takes on the identity of a friend or relative, usually female, who comes for a visit: my friend, my little friend, my aunt, my grandmother, Mother Nature, Miss Rachel, Sophie, or Mary Lou.

my unconverted friend (n.)

(US) a revolver, a pistol.

1869

‘South-Western Sl.’ in Overland Monthly (CA) Aug. 126: Among the names of revolvers I remember the following: Meat in the Pot, Blue Lightning, Peacemaker, Mr. Speaker, Black-eyed Susan, Pill-box, My Unconverted Friend.

SE in slang uses

In phrases

friend of Dorothy(’s) (n.)

see Dorothy’s friend n.

friend of Oscar (n.) [the gay icon, playwright Oscar Wilde (1854–1901)]

a male homosexual.

1999		(con. 1927) S. Selvadurai Cinnamon Gardens (2000) 111: They’re, you know ... inverts. ‘Friends of Oscar,’ as Aunt Ethel used to say.
1999		Guardian Sport 9 Apr. 16: He bowls from the Pavilion End [...] he’s a friend of Oscar.

friend of ours (n.)

(US und.) in speaking to a fellow Mafia gangster, a ‘made man’, a ‘soldier’ in a crime family.

1978

(con. 1971) R. Daley Prince of the City 96: ‘He [Bonnano Family capo Alphonse Indelicato] tells me, if you think he’s a rat, then you should kill him, but if you kill him you better be sure he’s a rat, because he’s a friend of ours.’.