December 24 is a notable one

EVE

Think of the word that often precedes "day" in celebrations or the night before a significant event.

December 24 is commonly known as Christmas Eve, so the clue hints at the word "Eve" as the last part of that phrase. The wordplay is straightforward—it’s asking for the term used to describe the evening before a notable day, like Christmas. In crosswords, "notable one" often points to a well-known example, making "Eve" the perfect fit.