The phrase "is in vain" denotes that something has failed to achieve its intended purpose. Other words and phrases that can be used as synonyms for "is in vain" include fruitless, futile, useless, ineffective, and unsuccessful. Other options include "to no avail," "without success," "unproductive," and "in vain effort." These terms can be used in a variety of contexts, including work, relationships, and daily life. If something is in vain, it implies that effort was put forth but ultimately failed to make a difference. Utilizing synonyms for this phrase can add depth and nuance to your writing or speech.