The most common and most likely answer to this crossword clue is the 13 letter word ANNIVERSARIES
I've seen this crossword clue in The Daily Telegraph
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More clues leading to the result ANNIVERSARIES
Buddy explains!
The straight part
We know that "special celebrations" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case special celebrations = anniversaries.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ANNIVERSARIES mean?
ANNIVERSARIES noun- A day that is an exact number of years (to the day) since a given significant event occurred. Often preceded by an ordinal number indicating the number of years.
- (loosely) A day subsequent in time to a given event by some significant period other than a year (especially as prefixed by the amount of time in question).