Crossword Genius

What the devil did is cruel (4)

Ross

I believe the answer is:

fell

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

'is cruel' is the definition.
(synonyms)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for fell that I've seen before include "High moorland or unforested hill in the UK" , "Stuck-up" , "Hide" , "to floor" , "Keeled over" .)

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.