You sure there aren't suites in those dorms? Or anything that would not be a simple 2-person dorm?
There are all kinds of units in them, from singles to four-person suites. Why would the term "dormitory" be limited to buildings with only doubles? The relevant sense in the OED is "In universities and colleges: a building in which students reside; a hall of residence; a hostel.
U.S." Curiously, it looks like "hall of residence" is the standard term for a dorm outside the US.
Also, like I said, not all frats are considered Greek Life. There are many fraternities not associated with the IFC (Intra-Fraternity Council...I think), thus not making them Greek life.
It looks like Allegheny has two inter-fraternity organizations, the Inter-Fraternity Council and the Panhellenic Council, which are associated with the male-only fraternities and the sororities, respectively. I don't think there are any frats at Allegheny not represented by one of these, nor does either represent an organization whose name isn't a bunch of Greek letters. Well, there are the honor societies. I'm a member of Phi Beta Kappa myself. But those aren't normally included in the term "fraternities" nor "Greek organizations". I'm nobody's brother.
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