Green’s Dictionary of Slang

(US) a wife.

1880		G.R. Sims Zeph (1892) 4: Take these, Zeph, as a little present to your frau.
1900		Bulletin (Sydney) 8 Dec. 4/2: Flit Kin was a small, worried Chow, and his frau was a tough lump of an Irish-woman, who ran him unmercifully.
1911		E. Dyson ‘At the Opera’ Benno and Some of the Push 90: He discovered a large, stolid-looking Dutch frau dumped on the seat directly behind.
1917		R. Lardner ‘Three Kings & a Pair’ in Gullible’s Travels 40: ‘Listen here,’ says the Frau. ‘Get this straight: Either Bess goes or I don’t go.’.
1926		J. Tully Jarnegan (1928) 151: His fat old frau nearly went crazy waiting for him.
1939		R. Chandler Big Sleep 122: There could be people who would know he was sweet on Eddie Mars’s frau.
1943		R.L. Bellem ‘Shakedown Sham’ Dan Turner – Hollywood Detective May 🌐 He figured his frau was in a jackpot of some sort, and he wanted to get her out of it.
1962		T. Berger Reinhart in Love (1963) 252: Fedder, as that he may be, was realistic enough to keep on good terms with his frau.