Skinny like a rabbit - maybe it's your uncle whatshisname (11)
I believe the answer is:
thingamybob
'whatshisname' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'skinny like a rabbit maybe it's your uncle' is the wordplay.
'skinny' becomes 'thin' (similar in meaning).
'like a rabbit maybe' becomes 'gamy' (I can't explain this - if you can you should give a lot more credence to this answer).
'it's your uncle' becomes 'Bob' (as in the phrase 'Bob's your uncle').
'thin'+'gamy'+'bob'='THINGAMYBOB'
Can you help me to learn more?
(Another definition for thingamybob that I've seen is " Unspecified object".)