Chiasmatic

Chiasmatic is an adjective used to describe structures, patterns, or processes that involve a crosswise or X-shaped arrangement, or that exhibit a reversal of order. The term derives from the Greek word chi, meaning 'cross', via the noun chiasma, used in various scientific and literary senses.

In literature and rhetoric, chiastic structures (often called chiasmus) place parallel elements in reverse order to produce balance or emphasis. A famous example is "Never let a Fool Kiss You or a Kiss Fool You," illustrating ABBA word order.

In anatomy, the optic chiasm is the X-shaped crossing of optic nerve fibers at the base of the brain. This chiasmatic configuration allows partial decussation, with fibers from the nasal retina crossing to the opposite hemisphere. Lesions can cause bitemporal hemianopia.

In genetics, chiasma or chiasmata refer to the physical sites of crossing-over between homologous chromosomes during prophase I of meiosis. The chiasmatic arrangement supports genetic recombination and variation.

The adjective is used across disciplines but is most common in discussions of rhetorical structure, neuroanatomy (optic chiasm), and genetics.