Dill, basil, marjoram, fennel seed, anise seed and angelica are all considered substitutes for tarragon. Frozen tarragon is a great substitute for fresh tarragon, and although dried tarragon will do in a pinch, it is not as flavorful.
Tarragon is a species of perennial herb in the Asteraceae family, and the one used as a culinary herb is a subspecies that is unique in its strong aroma. The rest of the family smells rather bland by comparison. As a culinary herb, it is particularly suited to chicken, fish and egg dishes. In parts of Russia, tarragon is used to flavor a popular soft drink.