define enigma:

 

e·nig·ma

/iˈniɡmə,eˈniɡmə/

noun

noun: enigma; plural noun: enigmas

1. a person or thing that is mysterious, puzzling, or difficult to understand.

   "Madeleine was still an enigma to him"

   h

   Similar:

   mystery

   puzzle

   riddle

   conundrum

   paradox

   problem

   unsolved problem

   question

   question mark

   quandary

   a closed book

   poser

   teaser

   brain-teaser

   stumper

1. 
   

Origin

mid 16th century: via Latin from Greek ainigma, from ainissesthai ‘speak allusively’, from ainos ‘fable’.

Use over time for: enigma