The nearest planet to the sun (7)
I believe the answer is:
mercury
'the nearest planet to the sun' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mercury that I've seen before include "Planet - rising with temperature?" , "one in distant orbit?" , "First planet from the Sun" , "First rock from the Sun - Hg" , "Element, symbol Hg" .)