According to Food Subs, dill seed and dill weed are not ideal substitutes for one another. Although dill seed and dill weed are from the same plant, they taste different. Dill seed is more pungent than dill weed.
Dill seed is ideal for use in breads, to flavor root vegetables and to add flavor to vinegar. Dill seeds are also used to make pickles. Dill weed is ideal for use in stews, to flavor fish and to add flavor to dips. According to Mother Earth Living, caraway seeds taste similar to dill seeds and can be interchanged in many recipes.