Might USA run up the planet? (6)
I believe the answer is:
uranus
'might usa run up the planet?' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for uranus that I've seen before include "Giant planet" , "world" , "Seventh planet from the sun" , "Planet that's the butt of much wordplay" , "Greek god ruler of universe, or a major planet" .)