A virtue of training pet (9)
I believe the answer is:
favourite
'pet' is the definition.
(I know that pet can be written as favourite)
'a virtue of training' is the wordplay.
'training' is an anagram indicator (to train can mean to grow something into a shape).
'a'+'virtue'+'of'='avirtueof'
'avirtueof' with letters rearranged gives 'FAVOURITE'.
(Other definitions for favourite that I've seen before include "Sir Walter Raleigh was one" , "that attracts lots of money" , "competitor thought likely to win" , "Beloved pet" , "royal confidant" .)