in the buff vs in the altogether

in the buff and in the altogether both are adjectives.

Word	Noun	Adjective	Verb	Adverb
in the buff	No	Yes	No	No
in the altogether	No	Yes	No	No

As adjectives, in the buff and in the altogether are synonyms defined as:

in the buff and in the altogether: (used informally) completely unclothed

Other synonyms of in the buff include bare-ass, bare-assed, in the raw, naked as a jaybird, peeled, raw, stark naked.

in the buff (adjective)	in the altogether (adjective)
(used informally) completely unclothed	(used informally) completely unclothed