Crane unit wobbling up in the air (9)
I believe the answer is:
uncertain
'up in the air' is the definition.
(similar in meaning)
'crane unit wobbling' is the wordplay.
'wobbling' indicates an anagram.
'crane'+'unit'='craneunit'
'craneunit' is an anagram of 'UNCERTAIN'.
(Other definitions for uncertain that I've seen before include "Changeable" , "Not definitely known" , "Doubtful, indecisive" , "up in the air" , "dubious" .)