What is the X in X-mas?
1580s, essentially a variant form of ambush (n.), representing a reborrowing of that French word after it had been Italianized. Ambuscade is from French embuscade (16c.), Gallicized from Italian imboscata, literally "a hiding in the bush," compounded from the same elements as Old French embuscher. Sometimes in English as ambuscado, with faux Spanish ending of the sort popular in 17c.