Ajwain, like all good spices, can be spelled a number of ways including ajwan or ajowan, none of which will register on your spell check. And if you live outside of India, you've probably never heard of it. It's also know as carom or bishops weed. Just to confuse things further it looks like caraway but is a member of the parsley family.
Ajwain has a very dominating flavour, and I reckon it's often one of the tastes of Indian food (like in samosa pastry) that people just can't work out how to replicate at home. Shubhra Krishan describes it best: "Let me tell you about ajwain, a warming and detoxifying spice. It tastes somewhat like thyme, but stronger. I find it somewhat like similiar to oregano, too. The best way to discover the distinct taste of ajwain, of course, is to sample it"
And sample it you should. Ajwain is heating, light and digestive. It stimulates Pitta and calms both Vata and Kapha. Ajwain has two main medicinal uses, it expels gas from the colon and is a natural painkiller, making it perfect for bloating or over eating. It stimulates the appetite and strengthens a weakened digestion. Secondly it is an expectorant and germicide, used in cases of coughs, colds, bronchitis, asthma, tonsillitis and throat infections. It is also antiparasitic, antiseptic, antispasmodic, carmitive, tonic and a general all round good guy.
There's some disagreement as to it's origin, but it is in common use today almost exclusively in India . Though it's sometimes found in North African spice blend Berebere. Like most spices, it's aroma compounds are lipophilic, meaning you ought to fry Ajwain in ghee to get the most flavour. Do try it, it's one of my favourites, but go easy, it can be very overpowering.