In medieval times, the English language was enriched by a large number of words coming from Old Norse, the language of the Vikings, and French, after the Norman conquest of 1066.
Words such as sky, skull, berserk, bull, cake, egg, fog, guest, kid, knife, knot, lad, mistake, plough, race, reindeer, saga, skin, skirt, wing, window, troll, they or verbs such as take, whirl, whisk, shake, haunt, hit are of Viking origin. Words beginning with “sk-” (e.g. skull, skill, sky, …) are typically Scandinavian; some of these words maintained the “sk-” sound, while others changed it into “sh-“, e.g. the verb “shall“, “sceal” in Old English and “skola” in Old Norse and Swedish.

After 1066, French became the language spoken at court and several words of French origin started to be used: beef, mutton, salad, sausage, cabbage, carrot, cherry, parish, prayer, mail, portcullis, friar, mass, dolphin, elephant, ostrich, falcon, state, guard, soldier, cavalry, officer, vault, belfry, aisle are just some examples we still use nowadays.