The word "quatercentennial" refers to a 400th anniversary, and while it may not be commonly used in everyday language, there are several synonyms that are more familiar. Some of these include quadricentennial, which has the same meaning as quatercentennial, but is more commonly used. Other options include four-century, four-hundredth, and 400th anniversary. These terms are clear and concise, making them more accessible to readers who may not be familiar with the more obscure term "quatercentennial." These synonyms can help better convey the meaning of celebrating a milestone that has taken 400 years to reach.