Mawson, C.O.S., ed. (1870–1938). Roget’s International Thesaurus. 1922.
Class IV. Words Relating to the Intellectual FacultiesDivision (II) Communication of Ideas
Section II. Modes of Communication
533. Secret.
ENIGMA, riddle, puzzle, nut to crack, conundrum, charade, rebus, logogriph; monogram, anagram, anagrammatism; Sphinx; crux criticorum [L.].
MAZE, labyrinth, meander [usually in pl.], Hyrcynian wood; intricacy.
PROBLEM (question) [See Inquiry]; paradox (difficulty) [See Difficulty]; unintelligibility [See Unintelligibility]; terra incognita [L.] (ignorance) [See Ignorance].
ENIGMATIC or enigmatical, anagrammatic or anagrammatical, monogrammatic, logogriphic, cryptic or cryptical.