The most common and most likely answer to this crossword clue is the 6 letter word RUEING
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The straight part
We know that "showing repentance" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case showing repentance = rueing.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 RUEING mean?
RUEING verb- To cause to repent of sin or regret some past action.
- To cause to feel sorrow or pity.
- To repent of or regret (some past action or event); to wish that a past action or event had not taken place.
- To feel compassion or pity.
- To feel sorrow or regret.