Fennel, also known as sweet anise, has a mild, sweet flavor that's similar to licorice. Popular in Italian and French cooking, it's often added to meatballs and sauces and pairs well with fish and seafood. But if you're out of anise and looking for that same flavor profile in a pinch, there are a number of substitutes you can use.
With a similar licorice flavor, anise seed can be used in place of fennel. Anise seed has a stronger flavor so make sure to use less in a recipe. Cumin, caraway seeds and dill can also stand in for fennel.
If your recipe calls for fresh fennel, you can use bok choy stems or celery stalks instead, although celery cooks faster. If you want to duplicate just the taste of fennel and not the volume, you can also use a teaspoon of fennel seed for each pound of fennel bulb needed in the dish.