mental reservation vs doubt

mental reservation and doubt both are nouns.

Word	Noun	Adjective	Verb	Adverb
mental reservation	Yes	No	No	No
doubt	Yes	No	Yes	No

As nouns, doubt is a hypernym of mental reservation; that is, doubt is a word with a broader meaning than mental reservation:

mental reservation: an unstated doubt that prevents you from accepting something wholeheartedly
doubt: the state of being unsure of something

Other hypernyms of mental reservation include doubtfulness, dubiety, dubiousness, incertitude, uncertainty.

mental reservation (noun)	doubt (noun)
an unstated doubt that prevents you from accepting something wholeheartedly	uncertainty about the truth or factuality or existence of something
	the state of being unsure of something

mental reservation (verb)	doubt (verb)
	consider unlikely
	lack confidence in