Goodbye to commercial that is classy (5)
I believe the answer is:
adieu
'goodbye' is the definition.
(synonyms)
'commercial that is classy' is the wordplay.
'commercial' becomes 'ad' (abbreviation for advertisement).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'classy' becomes 'u' (I've seen this in other clues).
'ad'+'ie'+'u'='ADIEU'
'to' is the link.
(Other definitions for adieu that I've seen before include "Farewell (French)" , "Farewell, Monsieur!" , "Fare thee well!" , "cheers" , "Goodbye, mademoiselle" .)