Model formerly fat? (7)
I believe the answer is:
example
'model' is the definition.
(I know that model can be written as example)
'formerly fat?' is the wordplay.
'formerly' becomes 'ex' (prefix meaning former or onetime).
'fat?' becomes 'ample' (I can't justify this - if you can you should believe this answer much more).
'ex'+'ample'='EXAMPLE'
Can you help me to learn more?
(Other definitions for example that I've seen before include "Instance, specimen" , "not the actual version" , "Thing characteristic of its kind" , "Something illustrating a general rule" , "Standard" .)