Yes, I know what cardamom is! You need it for gingerbread!

Cardamom is not very well known in the U.S. but it's an important spice in some Eastern cuisines and has been used and appreciated as a spice and medicinally for centuries. It's derived from the seeds of a plant (related to ginger) that grows in India, Sri Lanka, Java & Guatemala. It's what gives gingerbread and other spiced cookies their characteristic flavor. Cardamom's flavor is pretty much irreplaceable - there's very little else like it. It's best to purchase it fresh. It depends on what you are making as to what you might replace it with but I think that you will have to make a mixture of various things to try to approximate it's flavor. Tasted alone, it has a spicy slightly-biting taste. I have a jar of Chinese Five Spice flavoring by Sun Luck. (Each manufacturer of Five Spice flavorings has their own mixture.) This one that I have is made of Cinnamon, Anise, Fennel, Ginger, Clove and Licorice Root. Overall, it's flavor approximates cardamom.

Recently, I have seen recipes for Five Spice Gingerbread Cookies so we know that these flavors are complimentary. I've never had to try to replace cardamom - I've always gone to the trouble to find it for recipes that call for it - so I don't know if this information can help you at all, but Good Luck!