Admit adult leaving Greece (3,2)
I believe the answer is:
own up
'admit' is the definition.
(I've seen this before)
'adult leaving greece' is the wordplay.
'adult' becomes 'grown-up' (informal term for an adult).
'leaving' suggests deleting specific letters.
'greece' becomes 'gr' (abbreviation).
'grownup' with 'gr' removed is 'OWN UP'.
(Other definitions for own up that I've seen before include "Confess, admit guilt (3.2)" , "Confess, acknowledge fault" , "Admit to wrongdoing" , "be honest" , "Come clean (about wrongdoing)" .)