Is restful as a cat (4)

I believe the answer is:

naps

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

'is' is the definition.
Although both the answer and definition are verbs in their -s form, I can't understand how one could define the other.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for naps that I've seen before include "Tips; sleeps" , "Takes forty winks" , "Span including short sleeps" , "Snoozes" .)

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.