Etymology
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T-shirt (n.)
1920, in reference to the shape it makes when laid out flat (t-shirt is thus incorrect).
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T and A (n.)
1972, short for tits and ass (a phrase attributed to Lenny Bruce), in reference to salacious U.S. mass media; earlier it was medical shorthand for "tonsils and adenoids" (1942).
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T 

twentieth letter of the English alphabet; in the Phoenician alphabet the corresponding sign was the 22nd and last; everything after T in the modern alphabet represents European alterations or additions. The sound has been consistent throughout its history.

In Late Latin and Old French, -t- before -e- and -i- acquired the "s" value of -c- and words appeared in both spellings (nationem/nacionem) and often passed into Middle English with a -c- (nacioun). In most of these the spelling was restored to a -t- by or in the period of early Modern English, but sorting them out took time (Edmund Coote's "English Schoole-maister" (1596) noted malicious/malitious) and a few (space, place, coercion, suspicion) resisted the restoration. 

To cross one's t's(and dot one's i's) "to be exact" is attested from 1849. Phrase to a T "exactly, with utmost exactness" is recorded from 1690s, though the exact signification remains uncertain despite much speculation. The measuring tool called a T-square (sometimes suggested as the source of this) is recorded by that name only from 1785. The T-cell (1970) so called because they are derived from the thymus. As a medieval numeral, T represented 160. A T was formerly branded on the hand of a convicted thief.

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shirt (n.)

Old English scyrte "skirt, tunic," from Proto-Germanic *skurtjon "a short garment" (source also of Old Norse skyrta, Swedish skjorta "skirt, kirtle;" Middle Dutch scorte, Dutch schort "apron;" Middle High German schurz, German Schurz "apron"), perhaps related to Old English scort, sceort "short," etc., from PIE root *sker- (1) "to cut," on the notion of "a cut piece." Lithuanian šarkas "shirt," Old Church Slavonic sraka "tunic," Russian soročka, Finnish sarkki "shirt" perhaps are from Germanic. 

Formerly of the chief garment worn by both sexes, but in modern use long only of that for men; in reference to women's tops, reintroduced 1896. Bloody shirt, exposed as a symbol of outrage, is attested from 1580s. To give (someone) the shirt off one's back is from 1771. To lose one's shirt "suffer total financial loss" is from 1935. To keep one's shirt on "be patient" (1904) is from the notion of (not) stripping down for a fight.

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shirt-sleeves (n.)
1560s, from shirt (n.) + sleeve (n.). Usually with the notion of "without a coat."
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T-bone (n.)
type of steak, 1916, so called from the T-shaped bone that runs through it. The verb meaning "to strike (another car, bus, etc.) from the side" is by 1970, from adjectival use in reference to crashes, attested from 1952, from the position of the two vehicles at impact.
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half-shirt (n.)
1660s, "shirt front," from half + shirt. In modern use, "shirt cropped high at the waist," 2000.
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Brown Shirt (n.)
generic term for "Nazi, fascist," especially of the thuggish sort, 1934, originally (1922) in reference to the German Sturmabteilung ("Storm Detachment"), Nazi party militia founded 1921; they were called Brown Shirts in English because of their uniforms.
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Black Shirt (n.)
also blackshirt, 1922, member of Fasci di Combattimento, Italian paramilitary unit founded 1919 by Mussolini; so called for their uniforms.
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