Green’s Dictionary of Slang

1. to eat.

1869		‘Why I Am a Bachelor’ in Temple Bar Mag. May 224: I can no more bring myself to believe in the faith or truth of a woman than I can ‘chow-chow’ with chop-sticks.
1880		Bulletin (Sydney) 26 June 3/1: Two hundred and twenty Mongolian aesthetics marched through the streets the other day [...] The heathens said ‘we us chow-chow’.
1896		Mirror of Life 25 Apr. 15/1: [W]e saw Julius M. and the ‘ex-champion jockey’ chow-chowing at the Excelsior.
1899		New Oxford Item (Gettysburg, PA) 7/2: ‘Chow-chow’ is a word which the chinaman took to the Philippines [...] It means ‘to eat,’ ‘eating’ or ‘food’.

2. (US) to speak (in a Chinese language).

1879

Nat. Police Gaz. (NY) 15 Nov. 14/4: I like to see the Chinese gamble and chow-chow each other in their beautiful tea-box talk.