What is the X in X-mas?
1570s, originally used of the great auk of Newfoundland (now extinct), shift in meaning to the Antarctic bird (which looks something like it, found by Drake in Magellan's Straits in 1578) is from 1580s. Of unknown origin, though often asserted to be from Welsh pen "head" (see pen-) + gwyn "white" (see Gwendolyn), but Barnhart says the proposed formation is not proper Welsh. The great auk had a large white patch between its bill and eye. The French and Breton versions of the word ultimately are from English.