In this mock oath attributed in comic fiction to sailors, timbers designates the pieces of wood composing the ribs, bends and frames of a ship’s hull, and the verb shiver means to break or split into small fragments (this verb is from a Germanic base meaning to split; the verb shiver in the sense of to shake slightly is unrelated).

The literal meaning of shiver my timbers is therefore (if this should be so) may my ship’s beams be broken into pieces.

One of the earliest occurrences of the phrase is from Netley Abbey (London, 1794), an “operatic farce” by William Pearce; Master MᶜScrape is talking with Gunnel, a coxswain:

– MᶜScrape. What, Gunnel! and where the devil have you been hiding yourself?
– Gunnel. We’ve been weathering many a tort gale, in beating about the Channel?
– MᶜScrape. Myself wou’d rather hear, you’d been beating about the French.
– Gunnel. Shiver my timbers so we have, messmate—D’ye spy these colours?—my tight one we have taken a frigate.

Gunnel also uses a shorter form:

Hoa! my timbers, I spy our Captain in the South West quarter.

William Davies, a playwright, had previously made a coxswain say split my timbers in The Man of Honour (London, 1786).

Several variants of the exclamation had appeared even earlier in two picaresque novels by the Scottish author Tobias Smollett (1721-71). When he wrote them, he had served as a naval surgeon in the Royal Navy and had lived in Jamaica, so that he most probably made his characters use authentic nautical swearing.

His fourth novel, The Life and Adventures of Sir Launcelot Greaves, first appeared serially in twenty-five consecutive issues of The British Magazine. Or, Monthly Repository for Gentlemen & Ladies (London), from the magazine’s inaugural issue, on 1^st January 1760, to 1^st January 1762; Smollett wrote:

Captain Crowe, whose faculty of speech had been all this time absorbed in amazement, now broke into the conversation with a volley of interjections: “Split my snatch-block!—Od’s firkin!—Splice my old shoes!—I have sailed the salt seas, brother, since I was no higher than the Triton’s taffril—east, west, north, and south, as the saying is—Blacks, Indians, Moors, Morattos, and Seapoys?—but, smite my timbers! such a man of war—”

– snatch-block: a block having a hole in one side to receive the bight of a rope
– od’s firkin: God’s small cask (od: a euphemism for God, used in exclamations such as od’s me!, od’s my life!, od’s blood! – firkin: a small cask)
– old shoes: anchor blocks
– Triton: the ship named Triton after the sea god
– taffril = tafferel: the upper part of the flat portion of a ship’s stern above the transom, ornamented with carvings
– Moratto = Mahratta: a member of the princely and military castes of the former Hindu kingdom of Maharashtra in central India
– Seapoy = sepoy: an Indian soldier serving under British or other European orders.

The same character also uses a variant with start, meaning to cause to break away:

Captain Crowe continued to ejaculate unconnected oaths, which, however, seemed to imply that he was almost sick of his new profession. “D—n my eyes, if you call this—start my timbers, brother—”

In his second novel, The Adventures of Peregrine Pickle. In which are included, Memoirs of a Lady of Quality (London, 1751), Smollett had used a variant with od, the euphemism for God; Commodore Hawser Trunnion, an old seaman, says to Peregrine:

“Odds my timbers! I love thee so well, that I believe thou art the spawn of my own body.”

The plural timbers was also used figuratively. For example, in Gleanings through Wales, Holland, and Westphalia, with views of peace and war at home and abroad (London, 1795), by the English writer Samuel Jackson Pratt (1749-1814), a Welsh seaman welcomes the author in his hut:

Perceiving my dripping situation, he said, “Come shipmate, doff your jacket, put on this rug, come to an anchor in that corner, warm your shivering timbers with a drop of this dear creature, which will make a dead fish speak like an orator.”