Meeting up? I hope I am correct. Sorry if I'm not.
Answer: Plethora is a noun. Tranquility is a noun. Conundrum is a noun.
Explanation:
Answer:
"Presently I heard a heavy footstep in my room--the step of an elephant it seemed to me--it was not like anything human."
Explanation:
A word that replaces a noun. Ex: John eats apples -> He eats apples.