What is another word for "secret"?

Roget's Thesaurus (1911) lists these synonyms for "secret": abditory, adytum, ambuscade, ambush, anagram, and, arcanum, back, background, between, bite, blend, blind, blinker, book, bridle, button, cave, charade, cloak, close, closet, cloud, concealed, concealment, confidential, conundrum, costive, costiveness, counsel, cover, crack, crux, crypt, curt, curtain, curtness, danger, dead, deceive.