Acorns are not nuts but to be honest, they definitely resemble them. The acorn is the fruit of the oak. Popular tree nuts are pistachio, Brazil, almond, walnut, cashew, hazelnut, and pistachio. Peanuts, sesame seeds and sunflower seeds are not nuts, they are legumes.
A tanoak tree is a hybrid cross between a chestnut and an oak tree. But then we have the question, is a chestnut a nut? The chestnut is a member of the oak and beech family. If you are allergic to chestnuts, you may consider this before eating tanoak acorns, but I've been teaching the art of eating acorns for over thirty years and I've yet to have anyone tell me they had an allergic reaction to acorns of any variety.
If you haven't tried leaching and eating acorns, I urge you to do so. Even in very small amounts, the acorn can add texture and flavor to many dishes.
Suellen Ocean is the author of Acorns and Eat'em, a how-to vegetarian cookbook and field guide for eating acorns. Find it here: http://www.amazon.com/Acorns-Eatem-How--Vegetarian-Cookbook/dp/1491288973