I am interested in knowing the secret meaning of the Greek letters of
the following:
1. Alpha Chi Omega
2. Alpha Delta Pi
3. Phi Sigma Sigma

Even if you can get just one, I would appreciate it!

Alpha Chi Omega - They chose Alpha to signify that they were the first
fraternity in the school of music at DePauw University, they chose
Omega believing this would be the LAST fraternity formed in the school
of music. 'Kai' was chosen, meaning 'and', or 'Beginning and End', or
'The First and Last'. 'Kai' was changed to 'Chi' so that it would be a
Greek letter.

http://www.alphachiomega.org/about_axo/main.asp

Alpha Delta Pi - They were originally known as the Adelphean Society,
from the Greek word for 'Sister'. Notice the key letters at the
beginning of the syllables there, ADelPhean, or Alpha Delta Pi. So
their letters technically stand for 'Sister'.

http://www.alphadeltapi.org/contentmanager/page.asp?webpageid=187

Phi Sigma Sigma - They were originally Phi Sigma Omega but found that
someone else had already registered that name, and there's not much
history available on why they chose PSO in the first place...

Hope that helps. :)

I don't know of secret meanings, but Alpha Chi Omega is simply
translated as Acho, Alpha Delta Pi as adp and Pi Sigma Sigma as PSS