altogether vs completely

altogether is a noun but completely is not a noun.

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

As adverbs, altogether and completely are synonyms defined as:

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

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

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

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