monotone vs decreasing monotonic

monotone is a noun but decreasing monotonic is not a noun.

Word	Noun	Adjective	Verb	Adverb
monotone	Yes	Yes	No	No
decreasing monotonic	No	Yes	No	No

monotone (noun)	decreasing monotonic (noun)
an unchanging intonation
a single tone repeated with different words or different rhythms (especially in rendering liturgical texts)

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