What is the X in X-mas?
"hazelnut," late 14c., from Anglo-French philber (late 13c.), from Norman dialect noix de filbert, in reference to St. Philbert, 7c. Frankish abbot, so called because the hazel nuts ripen near his feast day, Aug. 22 (Old Style). Weekley compares German Lambertsnuss "filbert," associated with St. Lambert (Sept. 17); also German Johannisbeere "red currant," associated with St. John's Day (June 24). The name is Old High German Filu-berht, literally "very bright."