Ajowan, ajwain, carom, or bishop's weed (someimes erroneously called lovage, a different species altogether) is an herb (Carum copticum) native to the Mediterranean area and used in Indian and Arabic cooking. It is sometimes added to Bengali spice mixtures such as panch phora, and is found in the Ethiopian spice concoction berebere, which has Indian and Arabic influences. In India, ajowan is often added to chutneys, curries, breads (particularly parathas), and legumes (especially lentils).
The plant is a tall annual which looks kind of like wild parsley, but what is eaten are the seeds. They are tiny, light brown or purple, resembling celery or cumins seeds in appearance: long and striped. Ajowan seeds are sold ground or whole. Ajowan is related to caraway and cumin but tastes somewhat like thyme but astringent, if you can imagine that. Like any spice, its strong aroma is enhanced by toasting, but use it sparingly; the flavour is strong.
Like many spices, ajowan contains aromatic compounds which are lipophilic (literally "fat-loving"), which means they dissolve better in fat than in water. In India ajowan is often used to flavour and perfume ghee (clarified butter), after which the flavour is efficiently and deliciously dispersed throughout the food. One preparation, called a tadka, is particularly common in South India. A mix of spices such as cumin, dill, and ajowan are fried in ghee until they are aromatic; garlic and asafetida and maybe grated ginger are then added. The whole is mixed into cooked lentils or rice or green vegetables, yielding a nutritious vegetarian dish.
Ajowan is also used in ayurvedic medicine to ease indigestion, asthma, diarrhoea and flatulence (making the marriage with legumes in Indian cuisine even more fortuitious). Ajowan contains the essential oil thymol, which is a potent fungicide and antiseptic.