The most common and most likely answer to this crossword clue is the 5 plus 1 letter word ETHIC -
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The straight part
We know that "principles" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case principles = ethic -.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 ETHIC - mean?
ETHIC - noun- A set of principles of right and wrong behaviour guiding, or representative of, a specific culture, society, group, or individual.
- The morality of an action.
- Moral, relating to morals.