Tranquillity surrounds current exam (5)
I believe the answer is:
resit
'exam' is the definition.
(as in resitting an exam)
'tranquillity surrounds current' is the wordplay.
'tranquillity' becomes 'rest' (I've seen this in another clue).
'surrounds' means one lot of letters goes inside another.
'current' becomes 'I' (physics symbol).
'rest' going around 'i' is 'RESIT'.
(Other definitions for resit that I've seen before include "repeated test" , "later exam" , "Exam taken again" , "tested again" , "second try at test" .)