The Clue 31/12 (abbr.)
The Answer NYE
The clue "31/12 (abbr.)" refers to the date December 31st, which is the last day of the year. People often celebrate this day with parties and fireworks, calling it New Year's Eve. The abbreviation for New Year's Eve is commonly written as "NYE." Therefore, "NYE" is the correct answer to the clue.