Many folk do not realize that long-distance trains stopped serving Grand Central in 1991, as a result of aggregating Amtrak to Pennsylvania Station.
It occurred to me to learn how a architect, those who design rail structures, refer to them. And as luck would smile upon me, after much searching, I found this comment in an architectural forum:
I am not a stranger to this struggle to define railroad structures. In writing a series of articles concerning the effort to save Great Northern's Blaine (Washington) station, a fierce skirmish over whether the structure was a station or a depot ensued.
As you can see, we ended up referring to the structure as "Blaine Station."
A final item of interest. Grand Central Terminal was designated as a National Historic Civil Engineering Landmark in 2012. A bronze plaque marking the landmark designation was formally dedicated on February 1, 2013 in conjunction with the Terminal's Centennial. Grand Central Terminal was also designated as a National Historic Landmark in 1976.