It grows shaky when there's a wind (5)
I believe the answer is:
aspen
'it grows shaky' is the definition.
The definition suggests a singular noun which matches the answer.
'when there's a wind' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'there's a wind' becomes 'pen' (I can't explain this - if you can you should give a lot more credence to this answer).
'as'+'pen'='ASPEN'
Can you help me to learn more?
(Other definitions for aspen that I've seen before include "Its leaves flutter in the slightest breeze" , "somewhere in Colorado" , "Trembler" , "Tree with shivering leaves" , "A poplar with shivering leaves" .)