Wind up girl, only about five (8)
I believe the answer is:
dissolve
'wind up' is the definition.
(I've seen this before)
'girl only about five' is the wordplay.
'girl' becomes 'dis' (I am not sure about this - if you are sure you should believe this answer much more).
'only' becomes 'sole' ('sole' can be a synonym of 'only').
'about' indicates putting letters inside.
'five' becomes 'v' ('V' can be a synonym of 'five').
'sole' enclosing 'v' is 'solve'.
'dis'+'solve'='DISSOLVE'
(Other definitions for dissolve that I've seen before include "Nullify" , "Close down" , "Pass into a solution" , "Change into liquid" , "Disperse or melt in liquid" .)