Green’s Dictionary of Slang

a smart, well-turned-out fellow; also in fig. use.

[1753		E. Haywood [bk title] Jenny and Jemmy Jessamy].
1768		E. Gaton Festivous Notes on ... Don Quixote 40: Robin Hood, the Pindar of Wakefield, with many others more modern, but equally meritorious, such as Jemmy Jessamy.
1807		Hazlitt Reply to the Essay on Population 231: The tall captain with his arm round the chambermaid’s waist, or Jemmy Jessamy lolling on the sofa with his mistress.
[1818		Morn. Post 10 Aug. 3/4: English opera [...] Wrench, as Jemmy Jessamy].
1829		Morn. Post 1 Oct. 3/3: A Jemmy Jessamy of a midshipman waited on his Lordship to solicit a lieutenancy.
1838		Crim.-Con. Gaz. 15 Dec. 135/3: The very pink of coxcomb he, / In short a Jemmy Jessamy.
1844		Thackeray Barry Lyndon (1905) 17: I question whether any of the jemmy-jessamies of the present day would do half as much in the face of danger.
1845		R.S. Surtees Hillingdon Hall I 170: He had a considerable cross of the dancing-master in him, and was considered one of the best ‘goers’ at Almack’s or the Palace. In short, he was a pretty Jemmy Jessamy sort of fellow.
1850		N. Devon Jrnl 7 Feb. 4/2: We cannot see either the wisdom or justice of that Jemmy Jessamy sort of scrupulosity.
1859		G.A. Sala Twice Round the Clock 111: Wondrously like ostriches, too, are Jenny and Jemmy Jessamy.
1860		Westmorland Gaz. 28 Apr. 2/5: The ‘nice young man‘ of every tea party [...] ‘Jemmy Jessamy’ of the Upper House.
1864, 1867, 1870		Hotten Sl. Dict.
1853		Pall Mall Gaz. 9 May 4/2: Mr Cape’s other ‘Romance’ [...] — ‘Jemmy Jessamy, the Runner’.