Lemon sumac is a popular ingredient used in Middle Eastern cuisine for adding a tangy, lemony flavor to dishes. However, if you don't have lemon sumac or can't find it at your local store, there are several synonyms that you can use instead. These include sumac powder, which is made from the dried berries of the sumac shrub and has a sour, tangy taste, as well as lemon zest, which adds a citrusy flavor to dishes. Other alternatives include citric acid and tartaric acid, which can be used in small quantities to add a sour taste to food. So, next time you're out of lemon sumac, don't worry - there are plenty of other options to choose from.