“Sir", name possibly used in class (7)
I believe the answer is:
seminar
'class' is the definition.
(seminar is a kind of class)
'sir name possibly' is the wordplay.
'possibly' indicates an anagram.
'sir'+'name'='sirname'
'sirname' anagrammed gives 'SEMINAR'.
'used in' acts as a link.
(Other definitions for seminar that I've seen before include "Group discussing" , "Symposium" , "Short intensive study course for marines" , "University discussion" , "University course" .)