intonation vs monotone

intonation and monotone both are nouns.

Word	Noun	Adjective	Verb	Adverb
intonation	Yes	No	No	No
monotone	Yes	Yes	No	No

As nouns, monotone is a hyponym of intonation; that is, monotone is a word with a more specific, narrower meaning than intonation:

Other hyponyms of intonation include intonation pattern, drone, droning, singsong.

intonation (noun)	monotone (noun)
the act of singing in a monotonous tone	an unchanging intonation
singing by a soloist of the opening piece of plainsong	a single tone repeated with different words or different rhythms (especially in rendering liturgical texts)
the production of musical tones (by voice or instrument); especially the exactitude of the pitch relations
rise and fall of the voice pitch

intonation (adjective)	monotone (adjective)
	of a sequence or function; consistently increasing and never decreasing or consistently decreasing and never increasing in value
	sounded or spoken in a tone unvarying in pitch