E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A masher. One who renders himself conspicuous by affectation of dress, manners, and speech. The word was first familiarised in London in 1881, and is a revival of the old word dudes (clothes). We have several derivations, as dudder, one who sells dress-pieces; duddery, a rag-shop; duddle, to wrap up warmly (Halliwell), etc. It is not of American origin.
I should just as soon expect to see Mercutio smoke a cigarette, as to find him ambling about the stage with the mincing manners of a dude.Jefferson: Century Magazine, January, 1890, p. 383.