Tell-tale weapon? (8)

I believe the answer is:

crossbow

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

'weapon?' is the definition.
(I know that crossbow is a type of bow)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for crossbow that I've seen before include "Old weapon wiht mechanism for firing bolt" , "Medieval weapon" , "Old weapon with mechanism for firing arrow" , "Old weapon of war" , "Weapon firing bolts" .)

I've seen this clue in The Sun.

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