Relax about current exam (5)
I believe the answer is:
resit
'exam' is the definition.
(as in resitting an exam)
'relax about current' is the wordplay.
'relax' becomes 'rest' (to relax is to have a rest).
'about' means one lot of letters goes inside another.
'current' becomes 'I' (physics symbol).
'rest' placed around 'i' is 'RESIT'.
(Other definitions for resit that I've seen before include "Enquiring intrusively (into person's affairs)" , "later exam" , "tested again" , "second exam" , "Exam taken again" .)