nobilis

Nobilis, nobile, a third-declension adjective of two terminations: nobilis for masculine and feminine, nobile for neuter, ablative singular nobili, genitive plural nobilium. The abstract noun is nobilitas and the opposite ignobilis.

Underneath it is gnobilis with the g worn away, from nosco, "get to know", so the first meaning is "knowable, well known" and only then "of a known family". That is the Roman social fact in the word: a nobilis was a man with a consul among his ancestors, a matter of public record rather than of manner or morals. The moral sense of "noble" is a medieval and English development, so do not read it back into Cicero. Notice too that nobilis and notice sit on the same root, and that ignoble and ignorant are two branches of the same negative.