What is "snag boat"

Snag \Snag\, n. [Prov. E., n., a lump on a tree where a branch has been cut off; v., to cut off the twigs and small branches from a tree, of Celtic origin; cf. Gael. snaigh, snaidh, to cut down, to prune, to sharpen, p. p. snaighte, snaidhte, cut off, lopped, Ir. snaigh a hewing, cutting.]

1. A stump or base of a branch that has been lopped off; a short branch, or a sharp or rough branch; a knot; a protuberance.

   The coat of arms Now on a naked snag in triumph borne.
   --Dryden.

2. A tooth projecting beyond the rest; contemptuously, a broken or decayed tooth.
   --Prior.

3. 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.

4. (Zo["o]l.) One of the secondary branches of an antler.

5. Any sharp protuberant part of an object, which may catch, scratch, or tear other objects brought into contact with it.

   Snag boat, a steamboat fitted with apparatus for removing snags and other obstructions in navigable streams. [U.S.]

   Snag tooth. Same as Snag, 2.

   How thy snag teeth stand orderly, Like stakes which strut by the water side.
   --J. Cotgrave.