Op·pen·hei·mer (?p??n-h??m?r), J(ulius) Robert 1904-1967. American physicist who directed the Los Alamos, New Mexico, laboratory during the development of the first atomic bomb (1942-1945).American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.Op·pen·hei·mer (?p??n-h??m?r), J(ulius) Robert 1902-1967. American physicist who directed the laboratory at Los Alamos, New Mexico, during the development of the first atomic bomb (1942-1945).The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.