vain — adjective
Meaning: unproductive or unsuccessful.
en vain — in vain; to no avail.
This phrase expresses the idea of an action that brings no result or benefit despite effort.
Example: Ils ont essayé de le convaincre en vain.
Translation: They tried to convince him in vain.
Collins French–English Dictionary
Author’s summary:
The French word vain means “unproductive” or “futile,” and the phrase en vain translates as “in vain” or “to no avail,” denoting an effort made without success.