sweatshirt n.

Old English swætan "perspire," also "work hard," from Proto-Germanic *swaitjan "to sweat," from the source of sweat (n.). Compare Frisian swette, Dutch zweeten, Danish svede, German schwitzen. Meaning "to be worried, vexed" is recorded from c. 1400. Transitive sense is from late 14c. Related: Sweated; sweating. Sweating sickness was a sudden, often-fatal fever, accompanied by intense sweating, that struck England 1485 and returned periodically through mid-16c., described in the original citation (a chronicle from 1502) as "a grete deth and hasty."

Middle English shirt, shirte, "garment for the upper body worn next to the skin," from Old English scyrte, from Proto-Germanic *skurtjon "a short garment" (source also of Old Norse skyrta, Swedish skjorta "skirt, kirtle;" Middle Dutch scorte, Dutch schort "apron;" Middle Low German schörte, Middle High German schurz, German Schurz "apron"), which is perhaps related to Old English scort, sceort "short," etc., from PIE root *sker- (1) "to cut," on the notion of "a cut piece."

OED notes that "the meaning of the word in OE. is obscure, as the only instance of its occurrence is a gloss in which the meaning of the Latin word was probably not understood." Lithuanian šarkas "shirt," Old Church Slavonic sraka "tunic," Russian soročka, Finnish sarkki "shirt" perhaps are from Germanic.

Formerly of the chief under-garment worn by both men and women, but in modern use it has long been only that for men; in reference to women's tops, the word was reintroduced 1896.

Bloody shirt, a blood-stained shirt exposed as a symbol of some outrage, to arouse indignation or resentment, is attested from 1580s, usually figurative. Shirt since late 14c. often has been figurative of one's goods or possessions, hence give (someone) the shirt off one's back (1771); lose one's shirt "suffer total financial loss" (1935). To keep one's shirt on "be patient" (1904) is from the notion of (not) stripping down for a fight.