Synonyms and Antonyms of closed book
something hard to understand or explain the couple's unorthodox marriage is definitely a closed book to those outside of the relationship Synonyms mystery, conundrum, enigma, head-scratcher, mystification, puzzle, puzzlement, riddle, secretRelated Words brainteaser, case, challenge, knot, matter, perplexity, poser, problem, stumper, trouble
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