horn fair, n. — Green’s Dictionary of Slang

horn fair n.

[Horn Fair was a real occasion, held annually from the 12C until 1768 at Charlton, Kent on St Luke’s day, 18 Oct; St Luke bearing the evangelistic sign of the Ox, and thus wearing horns n.; processions of revellers, all wearing horns and sometimes masks, walked from Cuckold’s Point near Deptford, to Charlton. For an extensive discussion of the actual Horn Fair see Ward, ‘A Frolic to Horn-Fair’ in Writings (1704), pp.194–222 (esp. 211–13 in which he attributes the custom to a dalliance of King John); Grose (1785, et seq.) and Ebsworth Roxburghe Ballads (VII pt. 1, pp.195–6)]

the state of being cuckolded; a fig. gathering of cuckolds.

1654		Mercurius Fumigosus 22 25 Oct.–1 Nov. 187: Of Gally-Foysts, and water Speeches, / Of Horn-fair Beasts in Sattin Breeches.
1659		Mercurius Democritus 10-26 Aug. 101: He being jealous of his fine Bird (not without cause) was frightned because she sung the tune of Horn-fair most odiously.
1667		Poor Robin Apr. n.p.: Men who have light-heel’d wives [...] yet refuse to contribute to the Cuckow’s maintenance [...] be summoned to Horn-fair, and there be dubbed Acteons Knights.
1685–8		‘Dyers Destiny’ in Chappell Roxburghe Ballads (1874) II 120: You shall dig Gravel the next Horn-Fair-Day, Basket and Pit-Axe I reckon to buy, For you are a Cuckold.
1700		N. Ward A Frolic to Horn-Fair 3: Then to take Boat and Land at Cuckolds-Point; and from thence [...] to Horn-Fair.
1707		Humours of a Coffee-House 10 Sept. 22: He’s a Gentleman that values no more the spending two or three Guineas [...] than a Citizen’s Wife does, to be well Kiss’d upon a Horn-Fair Day.
1719		in D’Urfey Pills to Purge Melancholy V 72: Some rich and brave flourishing Cuckolds were there, / That came in whole Droves, Sir, as if to Horn-Fair.
1722		‘Whipping Tom’ Of the Immodest Wearing of Hoop-Petticoats Pt I 39: The Wife designs to qualify her Husband for Horn Fair.
1785, 1788		Grose Classical Dict. of the Vulgar Tongue.
1794		T. Dutton (trans.) Art of Cuckoldom 128: They were preparing for a second ride to Horn-Fair!
c.1810		‘The Blind Sailor’ in Holloway & Black I (1975) 30: A landsman, one Jem Devonport / She convoy’d to horn’s fair.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.