Relax about initiation of important exam (5)
I believe the answer is:
resit
'exam' is the definition.
(as in resitting an exam)
'relax about initiation of important' is the wordplay.
'relax' becomes 'rest' (to relax is to have a rest).
'about' is an insertion indicator.
'initiation of' indicates taking the first letters.
The initial letter of 'important' is 'i'.
'rest' placed around 'i' is 'RESIT'.
(Other definitions for resit that I've seen before include "Exam taken again" , "Student's test" , "take another exam" , "second try at test" , "Take examination again" .)