Green’s Dictionary of Slang

arbour n.

[SE arbour, a shady retreat]

the female genital area.

[UK]Harris’s List of Covent-Garden Ladies 74: Her once maidenhead thicket, now grown to a fine bushy arbour surrounding the blissful cell of the blind sovereign of wanton sports.
[UK]Farmer & Henley Sl. and Its Analogues.