Milton, say, old favourite around (4)
I believe the answer is:
poet
'milton say' is the definition.
(I know this)
'old favourite around' is the wordplay.
'old' becomes 'o' (abbreviation).
'favourite' becomes 'pet' (synonyms).
'around' is an insertion indicator.
'o' placed inside 'pet' is 'POET'.
(Other definitions for poet that I've seen before include "Tope with a versifier" , "Ginsberg perhaps" , "Heaney or Yeats, say" , "Rhymer" , "Writer in verse form" .)