Which of the following best defines the word archaic?

The word "archaic" refers to something that is no longer in everyday use, often because it has been replaced by more current forms or ideas. It suggests a sense of being out of date or belonging to an earlier period that is no longer relevant. Therefore, the definition that aligns most closely with this meaning is "outdated."

The other choices do not capture the essence of "archaic." For example, "contemporary" implies current relevance and modernity, which is the opposite of being outdated. "Prehistoric" refers to a time period before written history, which is distinct from the concept of something being simply old or outdated. "Traditional" may denote customs or practices that have been passed down but do not necessarily indicate that something is outdated; tradition can still hold relevance in contemporary society. Thus, "outdated" is the most accurate definition of "archaic."