Ajwain is a spice unfamiliar to Europe so I've never cooked with it, although I've probably experienced it in Indian restaurant dishes.

Ajwain plant
Ajwain fruits
Dried ajwain fruits
Ajwain plant
Ajwain fruits
Dried ajwain fruits

Species:Trachyspermum ammi, t. copticum, carum copticum.
Egypt and Eastern Mediterranean.
The main cultivation areas are Iran and India.
Used Part:
Small, caraway-like fruits (sometimes incorrectly called "seeds").
Apiaceae (parsley family).
Bitter. Similar to thyme, but stronger, less subtle and more pungent.
"Ajwain" is the Romanised spelling of the Hindi ajvain which can be traced back to the Sanskrit word for "Greek". Most Indo-European languages have similar names, although the spelling is sometimes varied, e.g. Dutch ajowan, German adiowan. Some European and Western Asian languages relate ajwain to Egypt, e.g. Turkish Mısır anason "Egyptian anise" or Finnish Koptilainen kumina "Coptic caraway".
The Arabic name kamun al-muluki means "royal cumin", a term also used for the rare Indian spice black cumin.
Some names for ajwain reflect the medicinal use of the plant and in particular its thymol content, e.g. graines de thymol.
The etymology of the English name "bishop's weed" is unknown and this name should best be avoided as it is also used for other plants of the apiaceae family, e.g. aegopodium podagraria "ground elder" and ammi visnaga "toothpickweed". The English name "lovage seeds" is also a false reference, as is the Slovak name Ligurčekové semeno. Genus name trachyspermum is a Latin composite for "rough-seeded". Species name ammi is a Latinised reference to the alternative botanical name carum copticum "Coptic caraway".
Ajwain is uncommon in Europe and is used mostly in Central Asia, the Punjab and Gujarat. It also enjoys popularity in the Arab world and is found in the Ethiopian spice mixture berbere. The strong aroma of ajwain is enhanced by roasting or frying and it goes well with potatoes or fish, although legumes are the most important field of application.
Indian vegetarian dishes are commonly flavoured with ghee (perfumed butter fat) containing ajwain. As with most aromatic spice compounds, ajwain is lipophilic and dissolves much better in fat than in water. Thus, frying in ghee not only enhances the fragrance due to the high temperature but also extracts the flavour into the fat, allowing it to be dispersed throughout the food. Tadka dhal, a typical lentil recipe, starts with dried and washed lentils cooked with turmeric until tender. The lentil puree is then flavoured using salt and a tadka, a mixture of spices fried in ghee. Cumin, dill and ajwain seeds are fried until they turn brown and evolve a strong aroma, garlic or asafoetida (and possibly grated ginger) are added and after some more frying the tadka is poured over the cooked lentils. In South Indian cuisine, tadka-like preparations are applied to dried legumes and also to green vegetables and boiled rice.
Ajwain is much used as a medical plant in Indian Ayurvedic medicine, mainly as a remedy for diseases of the digestive tract. In the West, the ajwain extract thymol is used in medicines for cough and throat irritation.