Kashk is a traditional Persian ingredient that is made from strained yogurt. It is commonly used in Middle Eastern and Mediterranean cuisines to add a unique tangy and sour taste to dishes. There are several synonyms for the word "kashk" that can be used interchangeably in recipes. Some of the most common alternatives include sour cream, buttermilk, labneh, and whey. Each of these ingredients has a similar acidity and consistency to kashk, making them suitable substitutions in various dishes. It is important to note that while these ingredients can replace kashk in a recipe to some extent, they may not provide the exact same flavor profile.