Wild sea bounds long coasts of isthmus (9)

I believe the answer is:

ballistic

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'wild' is the definition.
(I've seen this in another clue)

I cannot understand how the rest of the clue works.

(Other definitions for ballistic that I've seen before include "Projectile" , "Like missiles" , "Relating to projectiles and their flight" , "Winsome deer" , "To do with the flight of projectiles - basic lilt (anag)" .)

I've seen this clue in The Daily Express.

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