c. 1200, "illustrious, distinguished, of high rank or birth," from Old French noble "of noble bearing or birth," from Latin nobilis "well-known, famous, renowned; excellent, superior, splendid; high-born, of superior birth," earlier *gnobilis, literally "knowable," from gnoscere "to come to know" (from PIE root *gno- "to know"). The prominent Roman families, which were "well known," provided most of the Republic's public officials.
Sense of "distinguished by splendor, magnificence, or stateliness" is from late 13c. Meaning "worthy of honor or respect " is from mid-14c. Sense of "having lofty character, having high moral qualities" is from c. 1600. Noble savage is "primitive man conceived of as morally superior to civilized man;" the phrase itself is from Dryden; the idea developed in the 18c.
I am as free as Nature first made Man,
Ere the base Laws of Servitude began,
When wild in Woods the noble Savage ran.
[Dryden, "Conquest of Granada," 1672]
A noble gas (1902) is so called for its inactivity or inertness; a use of the word that had been applied in Middle English to precious stones, metals, etc., that did not alter or oxidize when exposed to air (late 14c.), with noble in the sense of "having admirable properties" (c. 1300).