abundance vs plentitude

abundance and plentitude both are nouns.

Word	Noun	Adjective	Verb	Adverb
abundance	Yes	No	No	No
plentitude	Yes	No	No	No

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

abundance (noun)	plentitude (noun)
the property of a more than adequate quantity or supply	a full supply
(chemistry) the ratio of the total mass of an element in the earth's crust to the total mass of the earth's crust; expressed as a percentage or in parts per million
(physics) the ratio of the number of atoms of a specific isotope of an element to the total number of isotopes present