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Webster 1913 Edition

Noun.

[L.

decussatio

Act of crossing at an acute angle, or state of being thus crossed; an intersection in the form of an X;

as, the

decussation

of lines, nerves, etc.

Noun.

The act of crossing at unequal angles; the crossing of two lines, rays or nerves, which meet in a point and then proceed and diverge.

decussation ‎(plural decussations)

A crossing or intersection of lines etc. so as to form an X-shape.
- 1658: which being doubled at the angle, makes up the Letter χ, that is the Emphaticall decussation, or fundamentall figure. — Sir Thomas Browne, The Garden of Cyrus (Folio Society 2007, p. 167)