One thing to do when you break a bone (4)
I believe the answer is:
'one thing' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for wish that I've seen before include "Express a desire (upon a star?)" , "Desire, hope" , "Something desired" , "Desire (to pull this bone?)" , "whim" .)