Added to some soup only (4)

I believe the answer is:

upon

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

'added' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'some soup only' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'UPON' is hidden within 'soup only'.

'to' acts as a link.

Can you help me to learn more?

(Other definitions for upon that I've seen before include "mounted" , "Lying on top of" , "At a prescribed point in time" , "Carried - on top" , "On tope of" .)

I've seen this clue in the Evening Standard.

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.