Regan and Goneril - the second playing up with Medieval catapult (6)

I believe the answer is:

onager

I'm a little stuck... Click here to teach me more about this clue!

'catapult' is the definition.
('onager' can be a synonym of 'catapult')

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for onager that I've seen before include "Creature" , "donkey" , "Strangely, the wild ass might be orange" , "Asian wild ass - orange (anag)" , "Asiatic wild ass" .)

I've seen this clue in the Irish Times (Crosaire) and the Irish Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.