What is the X in X-mas?
1570s, from Latin colostrum "first milk from an animal," of unknown origin.
colostrum co·los·trum (kə-lŏs'trəm)
The first milk secreted at the time of parturition, differing from the milk secreted later by containing more lactalbumin and lactoprotein, and also being rich in antibodies that confer passive immunity to the newborn. Also called foremilk.