The Collaborative International Dictionary of English v.0.48:
enigma \e*nig"ma\ ([-e]*n[i^]g"m[.a]), n.; pl. enigmas
([-e]*n[i^]g"m[.a]z). [L. aenigma, Gr. a'i`nigma, fr.
a'ini`ssesqai to speak darkly, fr. a'i^nos tale, fable.]
1. A dark, obscure, or inexplicable saying; a riddle; a
statement, the hidden meaning of which is to be discovered
or guessed.
[1913 Webster]
A custom was among the ancients of proposing an
enigma at festivals. --Pope.
[1913 Webster]
2. An action, mode of action, or thing, which cannot be
satisfactorily explained; a puzzle; as, his conduct is an
enigma. Enigmatic