oil drying agent vs drier

oil drying agent and drier both are nouns.

Word	Noun	Adjective	Verb	Adverb
oil drying agent	Yes	No	No	No
drier	Yes	No	No	No

As nouns, drier is a hypernym of oil drying agent; that is, drier is a word with a broader meaning than oil drying agent:

oil drying agent: a substance that promotes drying (e.g., calcium oxide absorbs water and is used to remove moisture)
drier: a substance that promotes drying (e.g., calcium oxide absorbs water and is used to remove moisture)

Other hypernyms of oil drying agent include desiccant, drying agent, siccative.

oil drying agent (noun)	drier (noun)
a substance that promotes drying (e.g., calcium oxide absorbs water and is used to remove moisture)	an appliance that removes moisture
	a substance that promotes drying (e.g., calcium oxide absorbs water and is used to remove moisture)