500s, earlier haliday (c. 1200), from Old English haligdĂŚg "holy day, consecrated day, religious anniversary;
Sabbath," from halig "holy" (see holy) + dĂŚg "day" (see day);
in 14c. meaning both "religious festival" and "day of exemption from labor and recreation," but pronunciation and sense diverged 16c.
As an adjective mid-15c. Happy holidays is from mid-19c., in British English, with reference to summer vacation from school.