Green’s Dictionary of Slang

one’s favourite female companion.

1909		J. Ware Passing Eng. of the Victorian Era.
1933		J.T. Farrell Gas-House McGinty 356: He talked all day about moon, beer, and gettin’ a black Dinah to change his luck.
1937		A.W. Upfield Murder Down Under (1951) 47: Me dinah will sool ’em when the bank gets tired.
1951		D. Stivens Jimmy Brockett 31: We didn’t do much good for ourselves with the little dinahs, as we called them in those days.