Hidden a crane away (6)
I believe the answer is:
arcane
'hidden' is the definition.
(I've seen this in another clue)
'a crane away' is the wordplay.
'away' indicates an anagram (letters move away from their original places).
'crane' is an anagram of 'rcane'.
'a'+'rcane'='ARCANE'
(Other definitions for arcane that I've seen before include "Requiring secret or mysterious knowledge" , "Recondite" , "Mysterious, secret or obscure" , "Esoteric, mysterious" , "Abstruse, mysterious" .)