Space-saving letters (3)
I believe the answer is:
etc
'space-saving letters' 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 so on, briefly" , "'And the rest, in short (3)'" , "And so on, in brief" , "Etcetera (abbrev.)" , "And so forth (abbr)" .)