"Duck out" is an idiomatic expression used to describe the act of leaving unobtrusively or escaping from a situation suddenly. There are several synonymous phrases that can be used instead of "duck out," depending on the context. For instance, you can say "make a run for it," "slip away," "take a powder," or "make an exit." Other possible alternatives include "sneak out," "bolt," "abscond," "depart unnoticed," or "vanish into thin air." "Duck out" is often used informally to describe situations where one leaves without proper notice or explanation. These synonyms can help add variety to your writing or conversation and bring out the appropriate tone and mood.