The most common and most likely answer to this crossword clue is the 12 letter word SUPERNATURAL
I've seen this crossword clue in The Guardian
S
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Buddy explains!
The straight part
We know that "uncanny" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case uncanny = supernatural.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 SUPERNATURAL mean?
SUPERNATURAL noun- A supernatural being
- Supernatural beings and events collectively (when used with definite article: "the supernatural")
- Above nature; beyond or added to nature, often so considered because it is given by a deity or some force beyond that which humans are born with.
- Not of the usual; not natural; altered by forces that are not understood fully if at all.