A crane poorly hidden (6)
I believe the answer is:
arcane
'hidden' is the definition.
(I've seen this in another clue)
'a crane poorly' is the wordplay.
'poorly' indicates anagramming the letters (a poor spelling).
'crane' anagrammed gives 'rcane'.
'a'+'rcane'='ARCANE'
(Other definitions for arcane that I've seen before include "Recondite" , "cryptic" , "Abstruse, mysterious" , "deep" , "Requiring special knowledge" .)