Crossword Genius

Legal action idiot puts up with, losing pounds before appeal (9)

Ross

I believe the answer is:

assumpsit

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

'appeal' is the definition.
Both the answer and definition are singular nouns.
Maybe you can see an association between them that I can't see?

I don't understand the remainder of the clue.

Can you help me to learn more?

I've seen this clue in The Sunday Times and The Times.
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