regret vs ruefulness

regret and ruefulness both are nouns.

Word	Noun	Adjective	Verb	Adverb
regret	Yes	No	Yes	No
ruefulness	Yes	No	No	No

As nouns, regret and ruefulness are synonyms defined as:

regret and ruefulness: sadness associated with some wrong done or some disappointment

Other synonyms of regret include rue, sorrow.

regret (noun)	ruefulness (noun)
sadness associated with some wrong done or some disappointment	sadness associated with some wrong done or some disappointment

regret (verb)	ruefulness (verb)
decline formally or politely
express with regret
feel remorse for; feel sorry for; be contrite about
feel sad about the loss or absence of