A French stall, rickety (8)
I believe the answer is:
unstable
'rickety' is the definition.
(similar in meaning)
'a french stall' is the wordplay.
'a french' becomes 'un' ('a' in French).
'stall' becomes 'stable' (I can't justify this - if you can you should give a lot more credence to this answer).
'un'+'stable'='UNSTABLE'
Can you help me to learn more?
(Other definitions for unstable that I've seen before include "Not well-balanced, liable to wobble" , "Likely to collapse" , "Precarious or subject to change" , "Not mentally sound" , "Wobbly" .)