Attractive woman briefly claims the heart of William Tell (4)
I believe the answer is:
blab
'tell' is the definition.
(I've seen this in another clue)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for blab that I've seen before include "Divulge secret information" , "Spill the beans" , "Give away secrets" , "24 ac secrets in talk" , "Shoot one's mouth off" .)