The most common and most likely answer to this crossword clue is the 11 letter word PERFORATION
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More clues leading to the result PERFORATION
Buddy explains!

The straight part
We know that "a bore" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a bore = perforation.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 PERFORATION mean?
PERFORATION noun- The act of perforating or the state of being perforated.
- Any opening in a solid object.
- An abnormal opening in an organ, such as a rupture.
- A series of holes punched through something in order to assist in separating parts.
- That portion of a surface that remains after an open disk is removed from it.