Green’s Dictionary of Slang

swap n.

an act of exchange.

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Swop. An exchange.
1787		Burns ‘Epigram on Sad Occasion’ in Poetical Works (1871) 128: O Death, hadst thou but spar’d his life, [...] We freely wad exchang’d the wife [...] Ev’n as he is, cauld in his graff, / The swap we yet will do’t.
1811		Lex. Balatronicum [as cit. 1785].
1819		W. Scott Bride of Lammermoor 469: As for the pouther, I e’en changed it [...] for gin and brandy and it served the house mony a year—a gude swap too.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1830		W. Cobbett Rural Rides I 117: Lord Castlereagh [...] was accused of making a swap, as the horse-jockeys call it, of a writer-ship against a seat. It is barter, truck, change, dicker, as the Yankees call it, but as our horse-jockeys call it swap, or chop.
1833		W. Carleton Traits and Stories of Irish Peasantry III 347: I’m ready to make a fair swap wid him any day.
1851		M. Reid Scalp-Hunters II 286: Fair swop, they say, ain’t no stealin.
1862		J.R. Lowell Biglow Papers 2nd ser. (1871) 294/1: We’d better take maysures for shetting up shop, And put off our stock by a vendoo or swop.
1868		W.M. Baker New Timothy in Harper’s Mag. XXXVI 445/2: Not even the greasy cards can stand against the attractions of a swap of horses, and these join the group .
1879		A.J. Leavitt Body Snatchers 5: If you want me to hold my hush I must be in with the swap.

In phrases

get/have the swap (v.)

to be dismissed from one’s employment.

1889		Dead Bird (Sydney) 26 Oct. 7/4: The aristocratic female reported him to his boss, and the energetic youth received the swap at once.
1889–90		Barrère & Leland Dict. of Sl., Jargon and Cant.
1905		H.G. Wells Kipps (1952) 92: Every time I’ve had the swap I’ve never believed I should get another Crib .
1905		H.G. Wells Kipps (1952) 47: And there was a terrible something called the ‘swap,’ or the ‘key of the street’.