The most common and most likely answer to this crossword clue is the 3 letter word PAX
I've seen this crossword clue in The Times
P
A
X
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The straight part
We know that "peace" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case peace = pax.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 PAX mean?
PAX noun- A painted, stamped or carved tablet with a representation of Christ or the Virgin Mary, which was kissed by the priest during the Mass ("kiss of peace") and then passed to other officiating clergy and the congregation to be kissed. See also osculatory.
- Friendship; truce.
- The kiss of peace.
- A crucifix, a tablet with the image of Christ on the cross upon it, or a reliquary.
- A cry for peace or truce in children's games.
- (usually in the plural) A passenger; passengers.
- (usually in the plural, by extension, hospitality industry) A guest (at an event or function).