William Karush, 80, educator and scientist who wrote Webster's "Dictionary of Mathematics." Born in Chicago and educated at the University of Chicago, he worked on the Manhattan Project to build the atomic bomb, specifically solving mathematical physics problems in the design of the first nuclear reactor. He taught at his alma mater and at UCLA, USC and Cal State Northridge. Karush was also a research scientist for Ramo-Wooldridge Corp., the forerunner of TRW, and for the System Development Corporation in Santa Monica. On Saturday in Los Angeles of complications after surgery.