telling vs efficacious

telling is a noun but efficacious is not a noun.

Word	Noun	Adjective	Verb	Adverb
telling	Yes	Yes	No	No
efficacious	No	Yes	No	No

telling (noun)	efficacious (noun)
informing by words
an act of narration
disclosing information or giving evidence about another

telling (adjective)	efficacious (adjective)
producing a strong effect	marked by qualities giving the power to produce an intended effect
disclosing unintentionally something concealed	producing or capable of producing an intended result or having a striking effect
powerfully persuasive