They fasten hair (5)

I believe the answer is:

locks

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'hair' is the definition.
(locks can mean hair)

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

(Other definitions for locks that I've seen before include "Canal features" , "Secure fasteners for doors" , "raising devices for sailors" , "Door fasteners" , "Fastens - hair" .)

I've seen this clue in The Irish Independent and The Globe and Mail.

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