gentleness n.

early 13c., gentile, gentle "well-born, of noble rank or family," from Old French gentil/jentil "high-born, worthy, noble, of good family; courageous, valiant; fine, good, fair" (11c., in Modern French "nice, graceful, pleasing; fine, pretty") and directly from Latin gentilis "of the same family or clan," in Medieval Latin "of noble or good birth," from gens (genitive gentis) "race, clan," from root of gignere "beget," from PIE root *gene- "to give birth, beget," from PIE root *gene- "give birth, beget," with derivatives referring to procreation and familial and tribal groups.

Sense evolved in English and French to "having the character or manners of one of noble rank or birth," varying according to how those were defined. From mid-13c. in English as "gracious, kind" (now obsolete), manners prescribed for Christian or chivalrous nobility. From late 13c. as "courteous, polite, well-bred, charming;" c. 1300 as "graceful, beautiful." Meaning "mild, tender; easy; not harsh" (of animals, things, persons) is from 1550s. Older sense remains in gentleman, and compare gentile (adj.), an alternative form which tends to keep the Biblical senses of the Latin word (though gentle in Middle English sometimes meant "pagan, heathen"), and genteel, which is the same word borrowed again from French. From 1823 as "pertaining to the fairies."

word-forming element denoting action, quality, or state, attached to an adjective or past participle to form an abstract noun, from Old English -nes(s), from Proto-Germanic *in-assu- (cognates: Old Saxon -nissi, Middle Dutch -nisse, Dutch -nis, Old High German -nissa, German -nis, Gothic -inassus), from *-in-, originally belonging to the noun stem, + *-assu-, abstract noun suffix, probably from the same root as Latin -tudo (see -tude).