Green’s Dictionary of Slang

nib n.²

1. (also nib-cove) a gentleman.

1812		Vaux Vocab. of the Flash Lang. in McLachlan (1964) 254: nib: a gentleman, or person of the higher order. People who affect gentility or consequence, without any real pretensions thereto, are from hence vulgarly called Half-nibs or Half-swells; and, indeed, persons of low minds, who conceive money to be the only criterion of gentility, are too apt to stigmatize with the before-mentioned epithets any man, who, however well-bred and educated, may be reduced to a shabby external, but still preserves a sense of decorum in his manners, and avoids associating with the vagabonds among whom he may unfortunately be doomed to exist.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue [as cit. 1812].
1834		(con. 1737–9) W.H. Ainsworth Rookwood (1857) 168: He’s a rank nib.
1845		G.W.M. Reynolds Mysteries of London vol. 2 142: Nib-cove Gentleman.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1914		Sport (Adelaide) 21 Aug. 5/6: Olly G. [...] You were seen knocking about with a nib .
1925		N. Lucas Autobiog. of a Thief 35: He told people that I was a ‘young toff, a real nib.’.
1949		Wodehouse Mating Season 99: Ask any of the nibs who move in diplomatic circles.
1954		Wodehouse Jeeves and the Feudal Spirit 70: Apparently he’s a bit of a nib on old silver.

2. a smartly dressed young man.

c.1921

T. Norman Penny Showman 21: Tom! You didn’t half used to be a nib! Flash! Self-conceited little fellow, wasn’t you.

In derivatives

niblike (adj.)

smart, fashionable.

1834		(con. 1737–9) W.H. Ainsworth Rookwood (1857) 178: All my togs were so niblike and splash.
1864, 1867, 1870		Hotten Sl. Dict.
1881		Newcastle Courant 2 Sept. 6/5: When not togged for night work he was usually [...] neatly dressed and looked as ‘nib-like’ a man as one [...] could well look.

nibsome (adj.)

gentlemanly.

c.1838		G.W.M. Reynolds ‘The House Breaker’s Song’ in Farmer Musa Pedestris (1896) 122: Oh! who would chirp to dishonour his name, / And betrays his pals in a nibsome game / To the traps ? – Not I for one!
1840		G.W.M. Reynolds (trans.) V. Hugo Last Day of Condemned ’ in 4: Flare up, my nibsome coves, flare up.
1961		(con. 1920s) J. Sparks Burglar to the Nobility 10: The persons who were most understandably annoyed of all were my uncle frank and his acquaintance Mr Nibsome.

In compounds

nib cove (n.) [cove n. (1)]

a gentleman.

1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict.

nib sprig (n.)

a gentleman’s son.

1819

P. Egan Key to the Picture of the Fancy going to a Fight 20: [W]hy should not the Flue Faker enjoy the pleasures of a mill as well as the Nib Sprig?

In phrases

half-nibs (n.)

one who apes a gentleman.

1812

Vaux Vocab. of the Flash Lang. in McLachlan (1964) 254: nib: a gentleman, or person of the higher order. People who affect gentility or consequence, without any real pretensions thereto, are from hence vulgarly called Half-nibs or Half-swells; and, indeed, persons of low minds, who conceive money to be the only criterion of gentility, are too apt to stigmatize with the before-mentioned epithets any man, who, however well-bred and educated, may be reduced to a shabby external, but still preserves a sense of decorum in his manners, and avoids associating with the vagabonds among whom he may unfortunately be doomed to exist.