Enigma

1.

(Something very difficult to understand, a riddle, a perplexing matter, person, etc) ប្រស្នា, បណ្តៅ
Example: I've know him for many years but he remains something of an enigma to me.

1.

A dark, obscure, or inexplicable saying; a riddle; a statement, the hidden meaning of which is to be discovered or guessed.

2.

An action, mode of action, or thing, which cannot be satisfactorily explained; a puzzle; as, his conduct is an enigma.

Synonyms

1.

conundrum, mystery, problem, puzzle, riddle

Antonyms

1.

clue, key, resolution, solution