Right to enter exam? It's tough (9)
I believe the answer is:
resilient
'tough' is the definition.
(I've seen this before)
'right to enter exam?' is the wordplay.
'right' becomes 'lien' (legal right).
'to enter' is an insertion indicator.
'exam?' becomes 'resit' (as in resitting an exam).
'lien' placed inside 'resit' is 'RESILIENT'.
'it's' acts as a link.
(Other definitions for resilient that I've seen before include "Elastic" , "Quickly recovering" , "bouncing back" , "Hardy" , "Tough" .)