reply vs echo

reply and echo both are nouns.

Word	Noun	Adjective	Verb	Adverb
reply	Yes	No	Yes	No
echo	Yes	No	Yes	No

As nouns, echo is a hyponym of reply; that is, echo is a word with a more specific, narrower meaning than reply:

reply (noun)	echo (noun)
the speech act of continuing a conversational exchange	an imitation or repetition
a statement (either spoken or written) that is made to reply to a question or request or criticism or accusation	the repetition of a sound resulting from reflection of the sound waves
	a reflected television or radio or radar beam
	a close parallel of a feeling, idea, style, etc.
	a reply that repeats what has just been said