What is the X in X-mas?
1590s, "white of an egg," from Latin albumen "white of an egg," literally "whiteness," from albus "white" (see alb). The organic substance (which exists nearly pure in egg whites) so called from 1800, also known as albumin (1869, from French albumine).
albumen al·bu·men (āl-byōō'mən)
The white of an egg, which consists mainly of albumin dissolved in water.