It's actually axiomatic. I can't really prove or justify why one should be good or bad, or why they should be good or bad to one another. But that good is good and to be strived for is the staring point of the philosophy.
I don't define axioms. It is the general definition commonly used, as recorded (but not decided) by the dictionary. Do you in fact have a different definition?
They have the actual meaning that the majority or community gives them. But that isn't necessarily static. But you've shown no evidence that it's changed in this case. That's what I've always been saying.