Event where the number 12 is important, and a feature of 12 two-word answers in this puzzle

Question:

Length:

Similar Crossword Questions:

Number of times this puzzle's theme word appears diagonally in the grid (to complete the puzzle, shade those words plus the Down answers that begin where they meet)
Word that can precede the last word of the four longest puzzle answers
Number inaugurated into this puzzle's theme answers
Word needed to be added to 12 appropriately placed answers in this puzzle for their clues to make sense
Word that goes after the start of and before the end of the five longest answers in this puzzle
Word separated in this puzzle's six longest answers
The word, as suggested by the saying formed by the ends of this puzzle's four longest answers
Discussion group, and a word that can follow the ends of this puzzle's five longest answers
Coastal irregularities, and word anagrammed in this puzzle's four longest answers
Feature of this puzzle's theme answers?
The last word of this puzzle's five longest answers is a type of one
Word that can follow the starts of this puzzle's five longest answers
European acme, and word hiding in this puzzle's 5 longest answers
Driveway stuff (and word that's hidden in this puzzle's four longest answers)
Number of protons by which the elements in the four longest puzzle answers have been enhanced
Important trial figure, or what you'll be when you read this puzzle's other four longest answers
Wee hr., and a hint to a feature common to this puzzle's four longest answers
Final (and a word that can precede the first word of this puzzle's longest answers)
Word hidden in this puzzle's longest answers
Feature of six other long answers in this puzzle
Govern, or word that can follow the first word of the four longest puzzle answers
Word hidden backwards in this puzzle's eight longest answers
Quarrel ... or a feature of five answers in this puzzle
Feature of this puzzle's three long Down answers
Number of times the letter 'U' appears in each of this puzzle's eight longest answers