Green’s Dictionary of Slang

fatymus n.

also fatyma, fattyma, fattymus
[pig Lat.]

a fat man or woman.

1890
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1899
[UK]Farmer & Henley Sl. and Its Analogues.
[UK]Western Dly Press 31 Mar. 4: [advert] Signor fattymus daviesyus will play selections on his Grand Piano.