Initially pop up with favourite dummy (6)
I believe the answer is:
puppet
'dummy' is the definition.
(thesaurus)
'initially pop up with favourite' is the wordplay.
'initially' says to take the initial letters.
'with' is a charade indicator (letters next to each other).
'favourite' becomes 'pet' ('pet' can be a synonym of 'favourite').
The first letter of 'pop' is 'p'.
'p'+'up'+'pet'='PUPPET'
(Other definitions for puppet that I've seen before include "Doll on a string or rod" , "Toy (with strings attached?)" , "See 20" , "Manipulated figure" , "Small doll on strings" .)