A sealed instrument can refer to various legal documents that are executed and sealed by the parties involved. However, there are many synonyms for this phrase that can be used depending on the context. A few examples include "signed and sealed contract," "official document," "notarized agreement," "authenticated agreement," "witnessed legal obligation," and "executed instrument." These terms can be used interchangeably to describe any type of legally binding agreement that has been properly executed, sealed, and witnessed by the parties involved. So, when referencing such legal documents, it's always useful to know these synonyms in order to communicate more clearly and effectively.