[cotton1706]

Dis-cover means to uncover.

There were already some (like the Norsemen) who knew there were some lands to the west.

But the whole civilized world did not know until Columbus made landfall and returned.

That is the point when the continents to the west were uncovered, so to speak.

[Czech_Occidentalist]

Does Greenland count as part of America? There was a Catholic diocese in Greenland from the 12th to the 14th century. The civilized world definitely knew that Greenland existed.