echo vs emit

echo is a noun but emit is not a noun.

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

As verbs, emit is a hypernym of echo; that is, emit is a word with a broader meaning than echo:

Other hypernyms of echo include let loose, let out, utter.

echo (noun)	emit (noun)
an imitation or repetition
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

echo (verb)	emit (verb)
to say again or imitate	expel (gases or odors)
ring or echo with sound	express audibly; utter sounds (not necessarily words)
bring to mind	give off, send forth, or discharge; as of light, heat, or radiation, vapor, etc.