This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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n. Anatomy A crossing or intersection of two tracts, as of nerves or ligaments.

n. Genetics The point of contact between paired chromatids during meiosis, resulting in a cross-shaped configuration and representing the cytological manifestation of crossing over.

n. A crossing of two nerves, ligaments etc.

n. The contact point between the two chromatids of a chromosome during meiosis.

n. Same as chiasm.

n. an intersection or crossing of two tracts in the form of the letter X

"In this early poem – the first one in his Selected Poems – Heaney uses a rhetoric figure that for a considerable period would be his trademark: the 'chiasma', or crossing of themes."

chiasmata   

optic chiasma   

chiasm    thalami    SMA    optician    neuritis