pleasantness vs pleasance

pleasantness and pleasance both are nouns.

Word	Noun	Adjective	Verb	Adverb
pleasantness	Yes	No	No	No
pleasance	Yes	No	No	No

As nouns, pleasance is a hypernym of pleasantness; that is, pleasance is a word with a broader meaning than pleasantness:

pleasantness: the feeling caused by agreeable stimuli; one pole of a continuum of states of feeling
pleasance: a fundamental feeling that is hard to define but that people desire to experience

Other hypernyms of pleasantness include pleasure.

pleasantness (noun)	pleasance (noun)
the quality of giving pleasure	a fundamental feeling that is hard to define but that people desire to experience
the feeling caused by agreeable stimuli; one pole of a continuum of states of feeling	a pleasant and secluded part of a garden; usually attached to a mansion