The most common and most likely answer to this crossword clue is the 11 letter word INCANTATION
I've seen this crossword clue in The Daily Telegraph
I
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More clues leading to the result INCANTATION
Buddy explains!
The straight part
We know that "spell" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case spell = incantation.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 INCANTATION mean?
INCANTATION noun- The act or process of using formulas and/or usually rhyming words, sung or spoken, with occult ceremonies, for the purpose of raising spirits, producing enchantment, or creating other magical results.
- A formula of words used as above.
- Any esoteric command or procedure.