kosher

According to the AHD, "kosher" means "conforming to dietary laws; ritually pure." It has also come to mean, in the slang sense, "genuine, authentic" (AHD). The word is traced back ultimately to the Hebrew "kaser," meaning "fitting, proper," or "to be fitting, to proceed," and came through Ashkenazi Hebrew (koser) to Yiddish, and finally to English (AHD). Interestingly, the OED traces its earliest usage back to 1851, despite the centuries upon centuries of abiding by such dietary traditions that had passed before. Perhaps it is the case that English-speakers had no need for the word, or perceived no cultural need for it, until the mid-19th century.