enigma

Từ điển American Heritage Dictionary 4th

e·nig·ma (ĭ-nĭgʹmə)n.
1. One that is puzzling, ambiguous, or inexplicable.
2. A perplexing speech or text; a riddle. [Latin aenigma, from Greek ainigma, from ainissesthai, ainig-, to speak in riddles, from ainos, fable.]

• Từ đồng nghĩa / Synonyms:
  riddle, conundrum, brain-teaser, mystery, secret, closed book