OK, that moves the determination of morality to the person picking the word.
But the official dictionary definition of murder is:
1. The unlawful premeditated killing of one human being by another.
2. Verb: Kill (someone) unlawfully and with premeditation.
But I understand the point you were making with the word, so we have communicated.
Murder has been made unlawful BECAUSE it is unjust.
When murder is made lawful, it remains unjust.