Green’s Dictionary of Slang

1. to act in an aristocratic, ostentatious manner (towards); to boast.

1825		‘Shadrack, The Orangeman’ Universal Songster I 27: How dat fellow vat calls himself a Jew, and swells about coming from Duke’s Place, tinks vat he has done de Frenchman, tip’d him de smitch and all that.
1834		‘The Lecherous Irishman’ Luscious Songster 35: In Cork he had swell’d all the girls I declare.
1842		Comic Almanack May 316: Then he turns out a dandy complete, to swell up and down Regent Street.
1850		Life in Boston & N.Y. (Boston, MA) 7 Sept. n.p.: [He] swells around with the ballet girls and is ‘bully’ in all the brothels and drinking shops.
1872		‘Mark Twain’ Roughing It 222: What did you come swellin’ around that way for, and tryin’ to raise trouble?
1883		‘Mark Twain’ Life on the Mississippi (1914) 44: He would come home and swell around the town.
1897		‘Mark Twain’ Tom Sawyer, Detective 115: He’s been swelling around here with them a month; yes, sir, twelve thousand dollars’ worth of di’monds on him.
1910		Bulletin (Sydney) 15 Dec. 39/3: Now Tim, by raison av his rapidly accumulatin’ bank-account, put on more dog than many an inspecthor. He swelled round in a silk vest an’ tie av a chaste vermilion and yellow hue [...].
1928		Hecht & MacArthur Front Page Act I: A lot of lousy, daffy, buttinskis, swelling around with holes in their pants, borrowing nickels from office boys.
1930		M. Fiaschetti You Gotta Be Rough 37: [I] made a remark or two that might indicate I had solved the mystery by some masterpiece of intellect beyond their comprehension. It’s fun to swell around .
1943		W.R. Burnett Nobody Lives for Ever 129: He wanted to dress up in his best and swell around the hotel; maybe order champagne in the dining room and take a gander at the upper-class chilis.

2. (US) to promote, to praise.

1896

F. Hutcheson Barkeep Stories 166: ‘I been huntin’ on de level, but I ain’t stuck on de game. Dem guys dat’s been swellin’ it up to me round here kin have it’.

3. to exaggerate.

1899

W.J. Kountz Billy Baxter’s Letters 38: Jim, I’m not swelling this a bit. On the level, it happened just as I write it.