The most common and most likely answer to this crossword clue is the 10 letter word LILY-WHITE
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The straight part
We know that "blameless" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case blameless = lily-white.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 LILY-WHITE mean?
LILY-WHITE adjective- A shade of the color white.
- Pure, unblemished, immaculate.
- Innocent, having a reputation beyond reproach.
- (sometimes derogatory) Caucasian; white.