Pair swapping academy for university is definitely on (6)

I believe the answer is:

doable

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

'on' is the definition.
Both the definition and answer are adjectives. Maybe they are linked in a way I don't understand?

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

Can you help me to learn more?

(Other definitions for doable that I've seen before include "easy to achieve" , "Able to be carried out" , "Achievable, performable" , "possible" .)

I've seen this clue in The Guardian.

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.