Turkey's heavy weapons on the borders (4)

I believe the answer is:

hens

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'borders' is the definition.
Although both the answer and definition are plural nouns, I cannot understand how they can define each other.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for hens that I've seen before include "Female fowl" , "Female chickens" , "Birds kept for laying" , "Adult chickens" , "Female birds" .)

I've seen this clue in the Irish Times and the Irish Times (Crosaire).

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