lexical database vs MRD

lexical database and MRD both are nouns.

Word	Noun	Adjective	Verb	Adverb
lexical database	Yes	No	No	No
MRD	Yes	No	No	No

As nouns, MRD is a hyponym of lexical database; that is, MRD is a word with a more specific, narrower meaning than lexical database:

lexical database: a database of information about words
MRD: a machine-readable version of a standard dictionary; organized alphabetically

Other hyponyms of lexical database include electronic dictionary, machine readable dictionary, wordnet.

lexical database (noun)	MRD (noun)
a database of information about words	a machine-readable version of a standard dictionary; organized alphabetically