Green’s Dictionary of Slang

1. a husband.

1832		Satirist (London) 2 Dec. 390/2: ‘Philpotts, who, I see has got eighteen children, must be a powerful member of the new sect—in fact, I always thought him a proper-gander’.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1895		Crowe Aus. Sl. Dict. 31: Gander, a married man.

2. (US) a man or husband who is away from home, a ‘grass-widower’.

1859		Matsell Vocabulum 36: gander A married man not living at home with his wife.
1882		Dly Dispatch (Richmond, VA) 1 Nov. 3/3: The detective [...] pointed out to the newspaper-man [...] a ‘gander,’ a married man.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1938		E.S. Gardner ‘Leg Man’ in Ruhm Hard-Boiled Detective (1977) 216: You seem to think a middle-aged old gander is going to get a sweet, innocent girl to fall for just your own sweet self. Bunk!