A mountain — it'll spread across more than one country (13)

I believe the answer is:

multinational

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

'across more than one country' is the definition.
I can't tell whether this definition defines the answer.

'a mountain it'll spread' is the wordplay.
'spread' indicates anagramming the letters.
'a'+'mountain'+'itll'='amountainitll'
'amountainitll' with letters rearranged gives 'MULTINATIONAL'.

Can you help me to learn more?

(Other definitions for multinational that I've seen before include "Large company" , "Crossing country borders" , "big business" .)

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.