Green’s Dictionary of Slang

dowlas n.

[Doulas, near Brest, in Brittany, the eponymous name of a coarse kind of linen, much used in the 16C and 17C, and later a strong calico made in imitation of this; the sl. is more immediately linked to the character Daniel Dowlas, in George Colman’s play The Heir at Law (1797)]

a linen-draper.

[UK]Hotten Sl. Dict.
[UK]Sl. Dict.