Green’s Dictionary of Slang

a travelling carriage seating two or four, with the coachman or postilion riding one of the horses; thus as v., to convey in such a vehicle.

1757		F. Greville Maxims, Characters and Reflections 19: He was told of the late invention of post-chays, of their great expedition, conveniency and cheapness, provided one could get a fellow-traveller .
1824		R.B. Peake Americans Abroad I ii: A po-chay driver don’t mind old age.
1828		J. Thomson An Uncle Too Many I i: But what brought them down? – why, bless you! only think, – a post shay and four!
1837		Morn. Advertiser (London) 28 July 3/2: I was stan’ing in the way of the King’s po-chay and his Majesty said, ‘git out o’ that, you spalpeen’.
1840		Newry Teleg. 1 Oct. 4/2: Tumble up, po-shay lads — Hurrah for sally-port!
1841		Derry Jrnl 9 Nov. 4/2: Miss Beebe [...] entered a bright yellow po-chaise.
1857		T. Hughes Tom Brown’s School-Days (1896) 73: Sending three on ’em off next morning in a po-shay with a parish constable.
1871		G. Meredith Harry Richmond I 135: There was a saying in the county that to marry a Beltham you must po’chay her. [Ibid.] 158: ‘She’s past po’chaises’, Squire Gregory sighed.
1876		H.E. Malet Annals of the Road 154: I have seen a number of these yellow po’-chays in a carpenter’s yard at Cambridge.