A crane became hidden (6)
I believe the answer is:
arcane
'hidden' is the definition.
(thesaurus)
'a crane became' is the wordplay.
'became' indicates an anagram (I've seen 'become' mean this).
'crane' with letters rearranged gives 'rcane'.
'a'+'rcane'='ARCANE'
(Other definitions for arcane that I've seen before include "Mysterious, secret or obscure" , "deep" , "Mysterious like a crane" , "Esoteric, mysterious" , "Mysterious, understood by few" .)