Holding to what is right when nothing compels it. Nobility here is a description of conduct, not of rank.
Latin nobilis (well-known, notable, of high birth), from (g)noscere (to know); holding to what is right when nothing compels it, a word for conduct that outgrew its claim about rank.
Conduct rather than lineage — what a word for birth came to mean once the house decided rank was never the point.