1896, X-rays, translation of German X-strahlen, from X, algebraic symbol for an unknown quantity, + Strahl (plural Strahlen) "beam, ray." Coined 1895 by German scientist Wilhelm Conrad Röntgen (1845-1923), who discovered them, to suggest that the exact nature of the rays was unknown. As a verb by 1899. Meaning "image made using X-rays" is from 1934, earlier in this sense was X-radiograph (1899).

"woody tissue in higher plants," 1875, from German Xylem, coined from Greek xylon "wood" (see xylo-).

1851, from Greek xylon "wood" (see xylo-) + -ene.

before vowels xyl-, word forming element meaning "wood," from Greek xylon "wood cut and ready for use, firewood, timber; piece of wood; stocks, a plank, beam, or bench," in New Testament, "the Cross," a word of uncertain origin. It seems to correspond with Lithuanian šulas "post, pole, stave," Russian šulo "garden-pole," Serbo-Croatian šulj "block," Old High German sul "style, pole," Gothic sauls "pillar," but the exact relationship is unclear, and Beekes asks, "Was the word taken from a non-IE substrate language?"

1842, from Latinized form of Greek xylophagos "wood-eating;" see xylo- + -phagous.

1866, coined from Greek xylon "wood" (see xylo-) + phōnē "a sound" (from PIE root *bha- (2) "to speak, tell, say").

"surgical instrument for scraping bones," 1680s, from Greek xyster "a graving tool," from xyein "to scrape." Beekes compare Sanskrit ksnauti "to grind, whet, rub," Lithuanian skusti "to shave, plane." Perhaps from a PIE *kes- "to scrape."