A leading organisation... (15)

I believe the answer is:

alphabetisation

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

This could be a double definition.

'a leading' is the first definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps there's a link between them I don't understand?

'organisation' is the second definition.
(alphabetisation is a kind of organisation)

Can you help me to learn more?

I've seen this clue in The Daily Express.

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.