Is the father limber but not robust? (7)
I believe the answer is:
fragile
'not robust?' is the definition.
(I've seen this before)
'is the father limber' is the wordplay.
'is the father' becomes 'fr' (I can't justify this - if you can you should believe this answer much more).
'limber' becomes 'agile' (I've seen this before).
'fr'+'agile'='FRAGILE'
'but' acts as a link.
Can you help me to learn more?
(Other definitions for fragile that I've seen before include "Easily-damaged" , "Easily broken or damaged" , "Liable to break easily" , "Not robust" , "Weak" .)