Is bound is a phrase that means something is obligated or certain to happen. Synonyms for this phrase include obliged, compelled, destined, fated, required, and predetermined. When a person is obligated to do something, they are bound to do it, which can also be expressed as being duty-bound. The word "bound" can also be replaced by the word "guaranteed," meaning that something is bound to happen. Additionally, synonyms for "is bound" might include words like automatic, inevitable, and unavoidable. These words imply that something is going to happen no matter what, as if it was inevitable. Essentially, any word or phrase that describes someone being forced to do something can be considered a synonym for "is bound".