Proper noun

1. a borosilicate glass with a low coefficient of expansion; used for heat-resistant glassware in cooking and chemistry
   • 1957 Letter from the Corning Glasswear Factory. "We had a number of prior trademarks ending in the letters ex. One of the first commercial products to be sold under the new mark was a pie plate, and in the interests of euphonism the letter "r" was inserted between pie and ex, and the whole thing condensed to pyrex."