Green’s Dictionary of Slang

(UK Und.) of a prostitute, kept by a given client; also of the man who lives off a whore.

1727		J. Gay Beggar’s Opera II iv: Pray, Madam, were you ever in keeping? [Ibid.] III v: To Mrs. Diana Trapes, the Tally-Woman and she will make a good Hand on’t in Shoes and Slippers, to trick out young Ladies, upon their going into Keeping.
1822		Egan Life and Adventures of Samuel Hayward 34: Hayward might now be said to be in keeping; or in the slang phraseology of the day, he was a Fancy Man!
1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 107: Keeping, in [sic] —maintenance of a prostitute, who is foolishly supposed to be solely attached to her keeper; but men frequently receive the like support from high-flyer women.

(Irish) in hiding, i.e. ‘keeping oneself out of sight’.

1921		Patrick MacGill Lanty Hanlon (1983) n.p.: Kevin Roe was abroad, on his own keeping, a wanted man [BS].
1927		P. O’Donnell Islanders (1933) 175: Manus was overjoyed to shelter the man that was ‘on his keeping’.