Great-nephew, also known as grandnephew, refers to the son of one's niece or nephew. However, there are also other terms that can be used to refer to this relationship. One such term is "nephew once removed," which is commonly used in genealogy. Another synonym is "second nephew," as the great-nephew is two generations away from the main person. Other less commonly used synonyms include "nephew's son," "cousin's son," and "grand-niece's brother." Although there are various terms for great-nephew, the most commonly used ones are great-nephew and grandnephew, depending on preference and context.