penny vs subunit

penny and subunit both are nouns.

Word	Noun	Adjective	Verb	Adverb
penny	Yes	No	No	No
subunit	Yes	No	No	No

As nouns, subunit is a hypernym of penny; that is, subunit is a word with a broader meaning than penny:

penny: a fractional monetary unit of Ireland and the United Kingdom; equal to one hundredth of a pound
subunit: a monetary unit that is valued at a fraction (usually one hundredth) of the basic monetary unit

Other hypernyms of penny include fractional monetary unit.

penny (noun)	subunit (noun)
a coin worth one-hundredth of the value of the basic unit	a monetary unit that is valued at a fraction (usually one hundredth) of the basic monetary unit
a fractional monetary unit of Ireland and the United Kingdom; equal to one hundredth of a pound