atom bomb: a nuclear weapon in which enormous energy is released by nuclear fission (splitting the nuclei of a heavy element like uranium 235 or plutonium 239)
bomb: an explosive device fused to explode under specific conditions
pinopsida: most conifers: in some systems classified as a class (Pinopsida) and in others as a subdivision (Pinophytina); used in some classifications for one of five subdivisions of Gymnospermophyta