Two left arms waving? (7)
I believe the answer is:
similar
'two left arms waving?' is the definition.
Both the answer and definition are adjectives. Perhaps there's an association between them I don't understand?
This is all the clue.
(Other definitions for similar that I've seen before include "Having a close resemblance to" , "Resembling, like" , "Alike, resembling" , "Comparable" , "Of the same kind" .)