Ajwain plays a little like a greatest hits album of more common herbs and spices. It tastes unmistakably like thyme, but it's got some oregano-like pungency, a bite reminiscent of cumin, and an aftertaste that may remind you of anise. But ajwain is an assertive, distinct spice all its own. It pulls those flavors from their familiar grounds and combines them into something utterly new.
A member of the parsley family (the leaves are also edible), most ajwain today comes from India, and is widely used in a variety of dishes there. It also goes by the names carom and bishop's weed. It's another one of those spices used to treat a range of health problems.