Hoisin sauce is a tasty and popular condiment used in many Chinese and Vietnamese dishes. This thick, dark brown sauce has a sweet and salty flavor with a hint of garlic. However, if you do not have hoisin sauce on hand or want to try something new, there are several synonyms that you can use as a flavorful substitute. The most commonly used synonym for hoisin sauce is plum sauce, which has a similar sweetness and tartness. Other options include oyster sauce, sweet bean sauce, or black bean sauce, which all have a deep umami flavor. Whatever substitute you choose, make sure to adjust the quantities to achieve the desired flavor in your recipe.