Two left arms waving? (7)
I believe the answer is:
Here is my best explanation:
'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", "Of the same kind", "Appearing the same", "Like", "Resembling, like", "Akin", "Alike, resembling" and "Comparable".)