The most common and most likely answer to this crossword clue is the 14 letter word PHANTASMAGORIA
I've seen this crossword clue in The Guardian
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More clues leading to the result PHANTASMAGORIA
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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 PHANTASMAGORIA mean?
PHANTASMAGORIA noun- A popular 18th- and 19th-century form of theatre entertainment whereby ghostly apparitions are formed.
- A series of events involving rapid changes in light intensity and colour.
- A dreamlike state where real and imagined elements are blurred together.