Green’s Dictionary of Slang

lum tum adj.

(US) aristocratic, upper-class; thus fashionable.

1879		Times (Philadelphia, PA) 2 Feb. 5/3: If I had [a sealskin overcoat] I wouldn’t wear it [...] The lum-tum fellows promenade Broadway in jackets.
1879		Times (Philadelphia, PA) 23 Mar. 8/1: Music, the clatter of glasses [...] laughter and good cheer [...] Are you blue? That’s the lum-tum dose [...] the propah capah.
1880		Memphis Dly Appeal (TN) 3 Feb. 4/3: A brilliant theatrical star. / Like a meteor gleaming afar. / Went out on the road— / Lum-tum, a la mode.
1881		Gilbert & Sullivan in Patience [song title] ‘The Lum-tum swell young man’ .
1882		Nat. Police Gaz. (NY) 1 Apr. 7/4: [She] was seduced by a ‘lardy dah’ character of the ‘lum tum uppah ordaw don’t you know’.
1883		letter in Sporting Times 10 Feb. 7/2: The S.T. (the lum-tum paper of England).
1883		Boston (Lincs.) 10 Mar. 7/2: ‘I wish to buy a hat [...] I want something lum tum’.
1885		Brooklyn Union 28 July 5/3: ‘[D]o the perfectly correct lum-tum proper caper just as you do in the city [...] You know that we can be lum-tum just as well as you’.
1890		Kansas City Star (MS) 21 Jan. 4/3: Having shown ‘the four hundred’ of New York [...] what he can do in the way of a real swell lum-tum ball, Mr Ward McAllister [etc].
1890		Kansas City Star (MS) 23 July 6/2: Cheviot, silk, percale, jersey or sateen shirts [...] are more fashionable and lum-tum [...] than the flannel shirt.

In derivatives

lum-tum-tivity (n.)

aristocratic activities, standards.

1885

Brooklyn Union 28 July 5/3: Its handsome hotel, its aristocratic surroundings, and its general tone of lum-tum-tivity.