Green’s Dictionary of Slang

flashy, dandified, fashionable.

1886		Bristol Magpie 2 Jan. 9/1: [I]f the young lady masher would have more respect for herself, and not keep her masher butcher so late on the doorstep, Magpie would not have eyed her.
1889		Dead Bird (Sydney) 14 Dec. 7/1: A masher bookmaker and a callco-hawker had four lively rounds in the yard of a city pub. the other day.
1890		Globe (London) 7 Feb. 1, col. 4: What are umbrellas or masher canes to students immersed in Mill or Emerson [...] ? [F&H].
1892		H. Lawson ‘Billy’s “Square Affair”’ in Roderick (1967–9) I 225: He wanted clothes, a masher suit, he wanted boots and hat.
1910		Bulletin (Sydney) 13 Oct. 13/1: Bill was in a plight / How to make her foller; / Thought he’d look all right, / In a masher collar.