a special section of some law enforcement agencies trained and equipped to deal with especially dangerous or violent situations, as when hostages are being held (often used attributively): a SWAT team.
1796, Amer.Eng. and northern England dialect word, possibly an alteration of M.E. swap "to strike, smite" (see swap), ultimately of imitative origin. The noun is recorded from 1800. Swatter "instrument for swatting flies" is recorded from 1917.