Father - lively but delicate (7)
I believe the answer is:
fragile
'delicate' is the definition.
(I know that delicate can be written as fragile)
'father lively' is the wordplay.
'father' becomes 'fr' (abbreviation as in a priest's title).
'lively' becomes 'agile' (I've seen this in another clue).
'fr'+'agile'='FRAGILE'
'but' acts as a link.
(Other definitions for fragile that I've seen before include "Not robust" , "Delicate; easily broken" , "Easily broken or damaged" , "Breakable" , "Liable to break easily" .)