first cause vs causal agency

first cause and causal agency both are nouns.

Word	Noun	Adjective	Verb	Adverb
first cause	Yes	No	No	No
causal agency	Yes	No	No	No

As nouns, causal agency is a hypernym of first cause; that is, causal agency is a word with a broader meaning than first cause:

first cause: an agent that is the cause of all things but does not itself have a cause
causal agency: any entity that produces an effect or is responsible for events or results

Other hypernyms of first cause include causal agent, cause.

first cause (noun)	causal agency (noun)
an agent that is the cause of all things but does not itself have a cause	any entity that produces an effect or is responsible for events or results