Release head departing BBC (5)

I believe the answer is:

untie

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'release' is the definition.
(eg to untie restraints)

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

(Other definitions for untie that I've seen before include "Let loose" , "Release (knots)" , "resolve" , "Detach" , "Loosen ropes or knots" .)

I've seen this clue in The Sun and The Independent.

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