The Greek letter CHI looks like an X, and the terms chiasm and chiasmus describe a series of two lines of poetry (or sentences) in which the second line is an inversion of the first, e.g. abc/cba, or ab/ba.
An example from the book of Isaiah ch. 22:22 -
He will open [A] and none [B] will shut [C],
he will shut [C] and none [B] will open [A].
From Jeremiah 4:5 -
Broadcast [A]in Judah [B],
in Jerusalem [B] proclaim [A].