chiasm

In general: a crossing of 2 lines. In anatomy: A decussation or crossing of 2 fibrous bundles such as tendons, nerves, or tracts. In cytogenetics: The site at which 2 homologous chromosomes make contact (thus appear to be crossed) enabling the exchange of genetic material between such chromosomes during prophase of meiosis.

References

Stedman's Medical Dictionary 27th ed, Williams & Wilkins, Baltimore, 1999