Green’s Dictionary of Slang

a short person, thus a contemptible person.

1614		Jonson Bartholomew Fair IV vi: Sir, you are a Welsh cuckold, and a prating runt, and no constable.
1673		J. Wade Vinegar and Mustard A6: Away, away thou impudent Welch Runt, thou, thou comest from a Forraign Nation.
c.1698		B.E. Dict. Canting Crew n.p.: Runt a little, short, truss Man or Beast.
1700		‘The National Quarrel’ in Playford Pills to Purge Melancholy II 232: Shone a Welch Runt and Hans a Dutch Boor.
1711		J. Addison Spectator No. 108 n.p.: This overgrown runt has struck off his heels, lowered his foretop, and contracted his figure, that he might be looked upon as a member of this newly erected Society [F&H].
1722		S. Centlivre Artifice Act III: This City spoils all Servants: I took a Welsh Runt last spring whose Generation scarce ever knew the Use of Stockings.
1796		Grose Classical Dict. of the Vulgar Tongue (3rd edn) n.p.: Runt. A short squat man or woman: from the small cattle called Welsh runts.
1811		Lex. Balatronicum [as cit. 1796].
1907		J.W. Carr ‘Word-List from Hampstead, N.H.’ in DN III iii 198: runt, n. [...] 2. Stunted person. Also used as a nickname. ‘Jim’s a little runt.’ ‘Runt Varney is here.’.
1915		M.G. Hayden ‘Terms Of Disparagement’ in DN IV:iii 200: runt, a term of contempt applied to an old man or woman.
1926		Wood & Goddard Dict. Amer. Sl. 45: runt. A short or undersized man or woman.
1930		(con. 1918) J. Hanley German Prisoner 15: ‘Has that soft runt gone mad?’.
1936		R. Chandler ‘Goldfish’ in Red Wind (1946) 149: But he’s a nice little runt and somehow I believe him.
1948		S.L. Elliott Rusty Bugles I i: Yeah, you dirty little sawn-off troppo runt.
1951		D. Stivens Jimmy Brockett 280: He’s only a little sawn-off runt but he knows a few nice little bits of muslin.
1960		E. De Roo Big Rumble 134: You think you can take ’em all on by yourself, you little runt!
1970		J. Conaway Big Easy 196: The two men came on, walking with a fast outlandish shuffle like desperadoes [...] Carrie wanted to laugh. ‘Runts!’ she told the ticket collector.
1981		S. Berkoff Decadence in Decadence and Other Plays (1985) 9: You married the runt.
1996		P. Cornwell Cause of Death (1997) 63: And what if I fall in a snowdrift, you little runt?