"Yadda, yadda, yadda" (3)
I believe the answer is:
'yadda yadda yadda' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for etc that I've seen before include "'And the rest, in short (3)'" , "And so forth (abbr)" , "And so on, briefly" , "And so on, in brief" , "Etcetera (abbrev.)" .)