Farewell notice that is for all to see (5)
I believe the answer is:
Here is my best explanation:
'farewell' is the definition.
(adieu is a kind of farewell)
'notice that is for all to see' is the subsidiary indication.
'notice' becomes 'ad'.
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'for all to see' becomes 'u' (universal dvd certificate).
(Other definitions for adieu that I've seen before include "Goodbye, mon ami!", "Adios, Arrivederci", "See you later", "Goodbye in France", "Au revoir (to a kind friend?)", "Goodbye, monsieur", "Auf wiedersehen", "Parting greeting", "So long" and "Farewell, Monsieur!".)