A cat’s lost by flap (3)
I believe the answer is:
tab
'flap' is the definition.
(both can mean a small piece of material)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for tab that I've seen before include "Small flap - bill" , "The bill in a restaurant" , "Ring pull" , "Tag" , "Flap; meal bill" .)