[chi.as.ma] n, pl -ma.ta [NL, X-shaped configuration, fr. Gk, crosspiece, fr. chiazein to mark with a chi, fr. chi (x)] (1839) 1: an anatomical intersection or decussation--compare optic chiasma
2: a cross-shaped configuration of paired chromatids visible in the diplotene of meiotic prophase and considered the cytological equivalent of genetic crossing-over -- chi.as.mat. ic adj