Is fennel in the onion family? No. Contrary to what many believe, the fennel plant (Foeniculum vulgare) is actually within the carrot family, Apiaceae (1).
Uncooked, fennel has what can be described as a mild licorice flavor. Is licorice made from fennel? No, but if you enjoy black licorace you will most likely enjoy this gluten free vegetable. When cooked, the flavor becomes more delicate. In either scenario, it would not be spicy in the sense of having heat like a hot pepper.
Fennel may be good for you when it comes to certain phytonutrients, but not for antioxidants. The amount of antioxidant activity in fennel is quite low when compared to the vast majority of vegetables. Even baked white potatoes are a multiple higher.
USDA Database for the Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 - Prepared by Nutrient Data Laboratory, Beltsville Human Nutrition Research Center (BHNRC), Agricultural Research Service (ARS), U.S. Department of Agriculture (USDA) - May 2010