Sort of milkman (3)
I believe the answer is:
ilk
'sort' is the definition.
(ilk can mean a type or kind)
'of milkman' is the wordplay.
'of' indicates a hidden word.
'ILK' is hidden in the letters of 'milkman'.
(Other definitions for ilk that I've seen before include "Type of milksop" , "Kind, class" , "Disposition" , "Kind of silks" , "Sort or type of silks" .)