Quietude is a related term of gentleness.
As nouns the difference between quietude and gentleness
is that quietude is tranquility while gentleness is the state of being gentle.
quietude
English
Noun
(en-noun)
tranquillity
Synonyms
* (tranquility) peace, serenity, tranquility
gentleness
English
Noun
(es)
The state of being gentle.