The "Congo" - Amtrak's hold over of the PRR/PC's Congressional Limited NY-Washington train.
Maybe only sort of a nickname, but regulars used to call the Metroliner the "Metro," as in, "I'll meet you on the 8 o'clock Metro tomorrow."
I often took a 7:35am PHL origination to New York for business. Amtrak called it the Benjamin Franklin. We, and other regulars (many were daily commuters) called it "The Bennie." Great train. Stopped only at North Philly, Newark and New York (then slogged its way to Boston). It was scheduled into NYP at 9:10. It was often 10-15 minutes early. My destination was directly across 7th Avenue from Penn, so the meeting would be scheduled to start at 9am, "or whenever The Bennie gets in."