Nigella is the small, jet-black, angular seed of Nigella sativa, an annual flower of the buttercup family grown across the Middle East and South Asia and known by a tangle of names — kalonji, black seed, black caraway and, misleadingly, "black cumin" or "onion seed." Crush a few between your fingers and they smell of oregano and thyme tangled with raw onion and a peppery bite, finishing faintly bitter; scattered over naan or fried in hot oil they release that herbal-savoury aroma into the whole dish.