Day named for the sixth plant from the sun (8)
I believe the answer is:
saturday
'day named for the sixth plant from the sun' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for saturday that I've seen before include "It's Samedi in France" , "Day named after the planet of the rings" , "when many are out of work" , "Samedi or Sabato or Samstag" , "Jewish Sabbath" .)