Kindness is warm, caring behaviour towards other people. An act of kindness, thank you for your kindness, kindness costs nothing.
It is uncountable for the quality and countable for a particular act: a kindness, small kindnesses. The old phrase to do somebody a kindness is still current and slightly formal. Note kill somebody with kindness, meaning to overwhelm them with attention, and out of the kindness of your heart, meaning with no expectation of anything back. The adjective is kind, and kindly does double duty as both adjective and adverb.
1nounkindnessWarm, caring behaviour towards others.
“She was treated with enormous kindness by strangers.”
synonyms: compassion, generosity
2nounactA kind act.
“It was a kindness nobody had to do.”
Too few real examples of this word to estimate which sense is commonest.
kindness is a quality of character.
Old English cynd meant nature or family — the same root as kin and kind in the sense of a type. Kindness was originally behaving as one of your own kin would, which is a much more concrete idea than the modern word carries.
Middle English
kyndenesse
English, today
kindness
From Middle English kyndenesse, equivalent to kind + -ness.
Etymology from Wiktionary, CC BY-SA