The term 'really old' can be summarized by the crossword solution 'ANCIENT, ' which is a 7-letter word. ANCIENT is defined as something that is very old, often referring to a period of time in history. It is often used to describe things that are thousands of years old, such as artifacts or ruins. ANCIENT is also used to describe people or cultures that existed long ago. Therefore, the term 'really old' can be accurately summarized by the word 'ANCIENT.'