Soldier on horse of the greatest importance (9)

I believe the answer is:

paramount

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

'of the greatest importance' is the definition.
(I've seen this before)

'soldier on horse' is the wordplay.
'soldier' becomes 'para' (paratrooper).
'on horse' becomes 'mount' (mount is a kind of horse. I am not sure about the 'on' bit.).
'para'+'mount'='PARAMOUNT'

Can you help me to learn more?

(Other definitions for paramount that I've seen before include "Pre-eminent - movie maker" , "Of the greatest importance" , "Highest" , "Chief in importance, supreme" , "First" .)

I've seen this clue in The Independent.

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.