Smallage is a rather uncommon word, so it's perhaps not surprising that there are not that many synonyms for it. However, there are a handful of words that can be used as substitutes in certain contexts. One option is celery, which is a vegetable that is related to smallage and can be used in many of the same ways. Another choice is lovage, which is also another plant species that is closely related to smallage and has a similar flavor. Finally, some people might use the term wild celery as a synonymous term, although this is less common. Overall, while there aren't many synonym options, it's still possible to find alternatives to smallage if needed.