The most common and most likely answer to this crossword clue is the 10 letter word PERPETUITY
I've seen this crossword clue in The Times
P
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Buddy explains!
The straight part
We know that "Permanence" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case permanence = perpetuity.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 PERPETUITY mean?
PERPETUITY noun- The quality or state of being perpetual; endless duration; uninterrupted existence.
- Something that is perpetual.
- A limitation intended to be unalterable and of indefinite duration; a disposition of property which attempts to make it inalienable beyond certain limits fixed or conceived as being fixed by the general law.
- An annuity in which the periodic payments begin on a fixed date and continue indefinitely.