The most common and most likely answer to this crossword clue is the 10 letter word TUNNELLING
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Buddy explains!
The straight part
We know that "digging of underground passages" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case digging of underground passages = tunnelling.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 TUNNELLING mean?
TUNNELLING verb- To make a tunnel through or under something; to burrow.
- To dig a tunnel.
- To transmit something through a tunnel (wrapper for insecure or unsupported protocol).
- To insert a catheter into a vein to allow long-term use.
- To undergo the quantum-mechanical phenomenon where a particle penetrates through a barrier that it classically cannot surmount.
- The act of burrowing a tunnel.
- The practice of exploring tunnel.
- The quantum mechanical passing of a particle through an energy barrier.
- A type of fraud where assets and profits are transferred out of firms for the benefit of those who control them.
- A feature of the file system that allows files to preserve certain properties, such as creation date, even after being deleted and recreated.