Green’s Dictionary of Slang

1. the legs.

1751		Smollett Peregrine Pickle (1964) 180: I wish thee a prosperous voyage, and good cheer, my lad; my timbers are now a little crazy, d’ye see; and God knows if I shall keep afloat till such time as I see thee again.
c.1790		‘Patrick’s Day in the Morning’ Luke Caffrey’s Gost 3: But we made the Bugs for to remember, / The 17th of March when each brave member, / Did oil their hides with Irish timber.
1822		D. Carey Life in Paris 239: It will go hard with me if I don’t shiver his timbers, or scuttle his hull.
1838		‘Nights At Sea’ in Bentley’s Misc. Apr. 588: Well, then, you get your greasy commission, and let me keep my timbers.
1845		‘A Week in Oxford! in Bell’s Life in Sydney 15 Nov. 4/1: Luckily, the earth gave way only under one of Old Grimaldi’s hind timbers, and he managed to scramble up and save himself.
1866		Illawarra Mercury (Wollongong, NSW) 18 Sept. 4/1: A racehorse with damaged legs is described [...] as ‘done up in his pins’ and [...] ‘weak in his understanding,’ or ‘shaky in his timbers’.
1884		W.C. Russell Jack’s Courtship I 135: Well, smite my timbers!
1900		Boy’s Own Paper 10 Nov. 87: His lower timbers were adorned by heavy pilot-cloth pants.
1904		Berwicks. News (Scot.) 6 Sept. 2/5: Shiver my timbers [...] but you’re a rum sort o’ craft.
1950		S. Murphy Stone Mad (1966) 139: Then the hell of a sou’westerly gale began to blow. ‘That’ll shiver your timbers,’ said the skipper.
1994		(con. 1960s) G. Byrne Pictures in my Head 40: She told us she was a monkey’s uncle and the sun of a gun and that her timbers were shivering.

2. (US tramp) a beggar who poses as a pencil-seller.

1918		‘A-No. 1’ Mother of the Hoboes 43: The Rating Of The Tramps. 11 Timbers: disguised begging by selling pencils.
1927		‘Jargon of the Und.’ in DN V 465: timbers, Lead pencils; also, a tramp who sells them.
1931		Irwin Amer. Tramp and Und. Sl. 189: Timbers.– Tramps who beg under pretence of peddling pencils. Also the pencils carried by these tramps.
1949		Monteleone Criminal Sl. (rev. edn).

3. (US tramp) one who has a wooden leg.

1931

Irwin Amer. Tramp and Und. Sl. 189: TIMBERS.– [...] a wooden-legged man.