The word "eighteenth" refers to being in or related to the number 18, which is an integer that represents a count of one more than seventeen and two less than nineteen.
One is The Ice House, set in eighteenth century Ireland and Barbados, and the other is Operation Red Hand, set in Ireland during World War II. (writing.ie)
The term «sandwich» was first used in eighteenth century England at a gentleman's gaming club in London, and appeared in a newspaper article about John Montague, the fourth Earl of Sandwich. (fieryfoodscentral.com)
This imposing fireplace surround is an authentic reproduction of eighteenth century French style. (idealhome.co.uk)