cryptologist vs decoder

cryptologist and decoder both are nouns.

Word	Noun	Adjective	Verb	Adverb
cryptologist	Yes	No	No	No
decoder	Yes	No	No	No

As nouns, decoder is a hypernym of cryptologist; that is, decoder is a word with a broader meaning than cryptologist:

cryptologist: decoder skilled in the analysis of codes and cryptograms
decoder: the kind of intellectual who converts messages from a code to plain text

Other hypernyms of cryptologist include decipherer.

cryptologist (noun)	decoder (noun)
decoder skilled in the analysis of codes and cryptograms	a machine that converts a coded text into ordinary language
	the kind of intellectual who converts messages from a code to plain text