What is the X in X-mas?
1540s, "pertaining to a crown" (or, later, to one of the extended senses of Latin corona), from French coronal (16c.), from Latin coronalis, from corona (see crown (n.)).
coronal cor·o·nal (kôr'ə-nəl, kə-rō'nəl)adj.
Of or relating to a corona, especially of the head.
Of, relating to, or having the direction of the coronal suture or of the plane dividing the body into front and back portions.