Definition of "rebus"

I back him at a Rebus or a Charade against the best Rhymer in the Kingdom—has your Ladyship heard the Epigram he wrote last week on Lady Frizzle's Feather catching Fire—

1777, Richard Brinsley Sheridan, The School for Scandal, I.i

The prior [Will Bolton] used to come out here to hunt in summer and recreate himself, and his rebus—a barrel or tun shot through with a crossbow bolt—is set into the garden walls.

2020 March 5, Hilary Mantel, “Salvage: London, Summer 1536”, in The Mirror & the Light, London: 4th Estate, page 122

He [John Morton] was a learned man, and had a fair library, (rebussed with more in text and tun under it,) partly remaining in the possession of the late earl of Arundel.The spelling has been modernized.

1655, Thomas Fuller, “Section IV. To John Ferrars, of Tamworth Castle, Esquire.”, in James Nichols, editor, The Church History of Britain, […], new edition, volume I, London: […] [James Nichols] for Thomas Tegg and Son, […], published 1837, book IV, subsection 34 (The Death of Archbishop Morton. A.D. 1500.), page 539