Possible Clues:

• Explorer beheading one noted chap and another, leaving Northern Ireland
• Navigator loves Puccini, to an extent
• Columbus contemporary
• Amerigo -, fifteenth to sixteenth century explorer
• He demonstrated that what Columbus had discovered was not 6-Down
• His name gained New World prominence
• Explorer for whom America is named
• America is called after the Florentine navigator
• Explorer with some hiccups, eventually returning
• Discoverer of the Amazon's mouth