Ajwain, also called carom seed or bishop's weed, is the dried fruit of Trachyspermum ammi, a small annual of the carrot family grown across the Indian subcontinent, Iran and the Horn of Africa. The minute, ridged grey-green seeds carry an astonishing punch — they smell and taste overwhelmingly of thyme, sharp and medicinal, because they are rich in the very same compound, thymol — with a hot, bitter, peppery bite that mellows to a clean herbal warmth once bloomed in hot ghee.