'decussation' originates from Latin, specifically the word 'decussatio' or verb form 'decussare', where the root 'decuss-' is related to 'decem' (ten) and referred to the letter X (the Roman numeral for ten).

'decussation' passed into English from Late Latin/Medieval Latin 'decussatio' (and related forms); the sense referencing an X-shaped crossing was preserved as it entered scientific and anatomical usage in modern English.

Initially, it meant 'a crossing in the form of an X' (connected to the Roman numeral X for ten), and over time the term came to be used specifically for anatomical fiber crossings and botanical leaf arrangements while retaining the general X-crossing sense.