completely vs altogether

completely is not a noun while altogether is a noun.

Word	Noun	Adjective	Verb	Adverb
completely	No	No	No	Yes
altogether	Yes	No	No	Yes

As adverbs, completely and altogether are synonyms defined as:

completely and altogether: to a complete degree or to the full or entire extent; Completely or entirely

Other synonyms of completely include all, entirely, right, totally, whole, wholly.

completely (noun)	altogether (noun)
	informal terms for nakedness

completely (adverb)	altogether (adverb)
so as to be complete; with everything necessary	with everything included or counted
to a complete degree or to the full or entire extent; Completely or entirely	with everything considered (and neglecting details)
	to a complete degree or to the full or entire extent; Completely or entirely