Work out butt in the air (3,2)
I believe the answer is:
end up
'work' is the definition.
The answer and definition can be both related to change as well as being verbs in their base form.
Maybe you can see an association between them that I don't see?
'butt in the air' is the wordplay.
'butt' becomes 'end' (eg the butt or end of a cigarette).
'in the air' becomes 'up'.
'end'+'up'='END UP'
'out' acts as a link.
Can you help me to learn more?
(Other definitions for end up that I've seen before include "Eventually find oneself" , "finish ahead" , "Arrive eventually" , "head first" , "Arrive (at); finish (with)" .)