The most common and most likely answer to this crossword clue is the 12 letter word PERSPICACITY
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More clues leading to the result PERSPICACITY
Buddy explains!

The straight part
We know that "Discernment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case discernment = perspicacity.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 PERSPICACITY mean?
PERSPICACITY noun- Acute discernment or understanding; insight.
- The human faculty or power to mentally grasp or understand clearly.
- Keen eyesight.