The most common and most likely answer to this crossword clue is the 10 letter word SANCTIFIED
I've seen this crossword clue in The Daily Telegraph
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Buddy explains!
The straight part
We know that "as a saint" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case as a saint = sanctified.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 SANCTIFIED mean?
SANCTIFIED adjective- Made holy; set aside for sacred or ceremonial use.
- Sanctimonious.
- To make holy; to consecrate; to set aside for sacred or ceremonial use.
- To free from sin; to purify.
- To make acceptable or useful under religious law or practice.
- To endorse with religious sanction.