Explained or answered a mystery (6)
I believe the answer is:
solved
'explained or answered a mystery' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for solved that I've seen before include "Deciphered, worked out" , "Found the answer, to problem or puzzle" , "Cracked" , "Found a solution" , "Puzzled out" .)