in anatomy, "a crossing, an intersection," 1832, medical Latin, from Greek khiasma "two things placed crosswise," which is related to khiasmos (see chi, and compare chiasmus). In cytology from 1911. Related: Chiasmal.
22nd letter of the Greek alphabet, representing a -kh- sound (see ch). The letter is shaped like an X, and so the Greek letter name was used figuratively to signify such a shape or arrangement (as in khiasma "two things placed crosswise;" khiastos "arranged diagonally; marked with an X;" khiazein "to mark with an 'X', to write the letter 'X'"). Some dialects used chi to represent the -ks- sound properly belonging to xi; Latin picked this up and the sound value of chi in Latin-derived alphabets is now that of English X.
in grammar, "the arrangement of repeated, parallel, or contrasted words or phrases in pairs with inversion of word order," 1850, Latinized from Greek khiasmos "a placing crosswise, diagonal arrangement" (see chi).