where does the phrase blue moon come from
The suggestion has been made that the term "blue moon" for "intercalary month" arose by folk etymology, the "blue" replacing the no-longer-understood belewe,' to betray'. The original meaning would then have been "betrayer moon", referring to a full moon that would "normally" (in years without an intercalary month) be the full moon of spring, while in an intercalary year, it was "traitorous" in the sense that people would have had to continue fasting for another month in accordance with the season of Lent.