Specialist and former favourite? About right (6)
I believe the answer is:
expert
'specialist' is the definition.
(thesaurus)
'former favourite? about right' is the wordplay.
'former' becomes 'ex'.
'favourite?' becomes 'pet' ('pet' can be a synonym of 'favourite').
'about' indicates putting letters inside.
'right' becomes 'r' (common abbreviation).
'pet' placed around 'r' is 'pert'.
'ex'+'pert'='EXPERT'
'and' is the link.
(Other definitions for expert that I've seen before include "Master" , "Specialist, pundit" , "At the right moment" , "Person with great knowledge or skill, specialist" , "Person with special knowledge or ability" .)