“Decussate” works as either a verb or an adjective — it can describe things shaped like an “X,” or it can refer to the action of the crossing. The Latin “decussatus” means “divided crosswise,” but it also connects with the Latin “decussis,” which describes the figure X, which is the Roman numeral for 10. If a word beginning with “dec-” has a Latin root, it might be referring to something crossed, or to the number 10. In ancient Rome, December was originally the 10th month of the year.