Most Pi Phi chapters and alum clubs call at least one of their formals or semiformals "Beaux and Arrows". That's what we call our formal in the fall. We also have a winter Snowflake Semiformal (used to be a Pledge Ball before that terminology went out) and a Spring Semi. I wish that had a better name... I suppose I could make one.
At my campus pretty much all the sororities do 3 formals/year now. To answer your question about Chi O, the Chi O's here have a formal called Persephone's Ball and a semiformal called White Carnation. Theta has a Twin Stars formal, I know.
My boyfriend's fraternity (Pike) has never done a formal in the past, but they're adding one this year. Don't know what it's called. We're traveling to Maryland to see the Preakness!!!!!
sooo giddy about that!
Others I happen to randomly know:
Sigma Chi Sweethearts
KA Old South
Sig Ep.. I've been before, but I can't for the life of me remember the name
Sigma Nu White Rose (been to that one too)
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