Synonyms for In the buff:

adj.

au naturel (adjective)
naked as a jaybird.
naked (adjective)
peeled, in the raw, stark naked, raw, unclothed, in the altogether.

n.

in the buff (noun)
raw, peeled, bare-ass, naked as a jaybird, in the altogether, stark naked, unclothed, bare-assed, in the raw.