What is a tree, or a branch of a tree, fixed in the bottom of a river or other navigable water, and rising nearly or quite to the surface, by which boats are sometimes pierced and sunk called?

snag — A tree, or a branch of a tree, fixed in the bottom of a river or other navigable water, and rising nearly or quite to the surface, by which boats are sometimes pierced and sunk. (Webster's 1913.)

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