Seminar a hundred miss (5)
I believe the answer is:
class
'seminar' is the definition.
(I've seen this before)
'a hundred miss' is the wordplay.
'a hundred' becomes 'C' (Roman numeral).
'miss' becomes 'lass' (lass is a kind of miss).
'c'+'lass'='CLASS'
(Other definitions for class that I've seen before include "First-rate" , "Where one learns" , "period" , "Group - style" , "seminar" .)