vainとは何ですか?Not yielding the desired outcome; fruitless: a vain attempt. Lacking substance or worth: vain talk. Excessively proud of one's appearance or accomplishments; conceited.Archaic Foolish.in vain To no avail; without success: Our labor was in vain. in vain In an irreverent or disrespectful manner: took the Lord's name in vain.