Pronunciation: (kī-az'mu),[key] —n., —pl.-mas, -ma•taPronunciation: (-mu-tu).[key] 1. Anat.a crossing or decussation, as that of the optic nerves at the base of the brain.
2. Cell Biol.a point of overlap of paired chromatids at which fusion and exchange of genetic material take place during prophase of meiosis. Also,chi•asmPronunciation: (kī'az-um).[key]