First planet discovered using a telescope (6)
I believe the answer is:
uranus
'first planet discovered using a telescope' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for uranus that I've seen before include "Planet that's the butt of much wordplay" , "Seventh planet from the sun" , "Might USA run up the planet?" , "Uses profane language" , "Most ancient of Greek gods, and a major planet" .)