Popular one in academic period is temporary (7)
I believe the answer is:
interim
'temporary' is the definition.
('interim' can be similar in meaning to 'temporary')
'popular one in academic period' is the wordplay.
'popular' becomes 'in'.
'one' becomes 'i' (Roman numeral).
'in' indicates putting letters inside.
'academic period' becomes 'term' (I've seen this before).
'i' placed within 'term' is 'terim'.
'in'+'terim'='INTERIM'
'is' acts as a link.
(Other definitions for interim that I've seen before include "acting" , "Meanwhile" , ", I'm put in grave situation initially" , "Caretaker" , "Meantime; temporary" .)