What is the X in X-mas?
early 15c., "teaching, instruction," from Old French document (13c.) "lesson, written evidence," from Latin documentum "example, proof, lesson," in Medieval Latin "official written instrument," from docere "to show, teach" (see doctor (n.)). Meaning "something written that provides proof or evidence" is from early 18c. Related: Documents.
1640s, "to teach;" see document (n.). Meaning "to support by documentary evidence" is from 1711. Related: Documented; documenting.