Yeah after researching a little more turns out the word is used for both hello and good bye which in English the closest word would be something like
salutation. Now in Spanish the word saludos or buenas or in Hindi namaste could be used because they are interchangeable.
But probably the reason the word salutation was not used was because the word already appears in other places as ἀσπασμός so a different word was needed plus the literal word for χαίρω is Hail and it wasn't used either probably because it just doesn't sound right (Young's Literal Translation).
Now i did find an English word that would fit and is not found elsewhere in scripture or in any translation the word asylum. The word meaning a place of safety and protection (χαίρω as sense of safe, with impunity). Also in order to "share in his evil deeds" you would need to "welcome him in"
Examples:
"If anyone comes to you and does not bring this teaching, do not receive him into your house and do not offer him asylum, for the one who offers him asylum shares in his evil deeds."
"If anyone comes to you and does not bring this teaching, do not receive him into your house and do not welcome him in, for the one who welcomes him in shares in his evil deeds."
Note: Now me personally would not use it but if i where trying to convey meanings then it would get the point across, but regardless Johns point to the Elect Lady is clear don't fellowship with Gnostics. What a contrast to Pauls attitude toward Gnostics 2Tim 2:24-26 And the servant of the Lord must not strive; but be gentle unto all men, apt to teach, patient, In meekness instructing those that oppose themselves; if God peradventure will give them repentance to the acknowledging of the truth; And that they may recover themselves out of the snare of the devil, who are taken captive by him at his will.