Small, black nigella seeds are a confusing spice to many people because of the many names they go by. In India they are known as kalonji and in the United States they are called charnushka. They are also frequently (and mistakenly) called black onion seeds, black cumin and black caraway. However, they have no relationship to cumin, caraway or onions (apart from flavour), and are very much their own spice.
Nigella seeds are hard and crunchy with a flavour like toasted onions. They are dry roasted in India and used on flatbreads like naan and they are particularly good with potatoes and root vegetables. They are also one of the five spices that make up panch poran, a spice mixture from Bengal.