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' means one lot of letters goes inside another.
'exam?' becomes 'resit' (as in resitting an exam).
'lien' going within '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" .)