Horrible toadies purchasing Queen 'rock' (8)
I believe the answer is:
asteroid
'rock' is the definition.
(an asteroid is a rock in space)
'horrible toadies purchasing queen' is the wordplay.
'horrible' indicates an anagram.
'purchasing' means one lot of letters goes inside another (some letters take possession of others).
'queen' becomes 'r' (abbreviation for regina, e.g. in ER ).
'toadies' with letters rearranged gives 'asteoid'.
'asteoid' enclosing 'r' is 'ASTEROID'.
(Other definitions for asteroid that I've seen before include "Minor planet" , "Small body orbiting sun" , "Bit of rock that moves around the heavens" , "Ceres, say" , "could be dangerous for astronauts" .)