To sink below the surface of the water: The ship struck a reef and foundered. To cave in; sink: The platform swayed and then foundered. To fail utterly; collapse: a marriage that soon foundered. To stumble, especially to stumble and go lame. Used of horses. To become ill from overeating. Used of livestock. To be afflicted with laminitis. Used of horses. To cause to founder. See laminitis. One who establishes something or formulates the basis for something: the founder of a university; the founders of a new nation.