mnemonist vs expert

mnemonist and expert both are nouns.

Word	Noun	Adjective	Verb	Adverb
mnemonist	Yes	No	No	No
expert	Yes	Yes	No	No

As nouns, expert is a hypernym of mnemonist; that is, expert is a word with a broader meaning than mnemonist:

mnemonist: an expert in the use of mnemonics; someone able to perform unusual feats of memory
expert: a person with special knowledge or ability who performs skillfully

mnemonist (noun)	expert (noun)
an expert in the use of mnemonics; someone able to perform unusual feats of memory	a person with special knowledge or ability who performs skillfully

mnemonist (adjective)	expert (adjective)
	having or showing knowledge and skill and aptitude
	of or relating to or requiring special knowledge to be understood