A riddle, or a difficult problem.
A species of grasshopper, Oedaleonotus enigma.
Mysteriousness; obscurity; lack of clarity.
The Talaud kingfisher, Todiramphus enigma.
A rare species of moth, Heliothis enigma.
A style of literature characterized by obscurity and hints of transcendental meaning.
Something or someone puzzling, mysterious or inexplicable.
A protein with three LIM domains (a conserved cysteine- and histidine-rich structure of two adjacent zinc fingers) at the C terminus that regulates protein phosphorylation.
Riddles and puzzles, collectively.
A problem that is challenging to solve.
Used other than figuratively or idiomatically: see hard, nut, crack.
A situation, person, group, etc. which is difficult to overcome or deal with.
A place, opportunity, etc. to which it is difficult to gain entry.
An amount that is difficult to finance.