evidence vs smoking gun

evidence and smoking gun both are nouns.

Word	Noun	Adjective	Verb	Adverb
evidence	Yes	No	Yes	No
smoking gun	Yes	No	No	No

As nouns, smoking gun is a hyponym of evidence; that is, smoking gun is a word with a more specific, narrower meaning than evidence:

evidence (noun)	smoking gun (noun)
your basis for belief or disbelief; knowledge on which to base belief	indisputable evidence (especially of a crime)
(law) all the means by which any alleged matter of fact whose truth is investigated at judicial trial is established or disproved
an indication that makes something evident

evidence (verb)	smoking gun (verb)
provide evidence for; stand as proof of; show by one's behavior, attitude, or external attributes
provide evidence for
give evidence