enigma

Definition of Enigma in English :

something that baffles understanding and cannot be explained

Example Sentences:
'how it got out is a mystery'
'it remains one of nature's secrets'

a difficult problem

WordNet Lexical Database for English. Princeton University. 2010.

Enigma

noun

a person, thing, or situation that is mysterious, puzzling, or ambiguous

noun

1.

a perplexing, usually ambiguous, statement; riddle

2.

a perplexing, baffling, or seemingly inexplicable matter, person, etc.

n. pl. e·nig·mas also e·nig·ma·ta (-mə-tə)

1. One that is puzzling, ambiguous, or inexplicable.

2. A perplexing speech or text; a riddle.