painlessness vs gentleness

painlessness and gentleness both are nouns.

Word	Noun	Adjective	Verb	Adverb
painlessness	Yes	No	No	No
gentleness	Yes	No	No	No

As nouns, gentleness is a hypernym of painlessness; that is, gentleness is a word with a broader meaning than painlessness:

Other hypernyms of painlessness include mildness, softness.

painlessness (noun)	gentleness (noun)
The quality of being free from pain, without pain or trouble.	acting in a manner that is gentle and mild and even-tempered
Ease; lack of difficulty.	the property possessed by a slope that is very gradual