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I thought this might be a motor start or run capacitor based on its size, but its markings aren't particularly revealing (to me).
Also I'm not sure if the resistor would be typical on a motor capacitor?
Unfortunately the stamped markings seem illegible, its not due to being a blurry photo (3rd image).
Lettering reads:
C800 (or C-800 or C•800)
KS 2018-1
CORNELL-DUBILIER
<patent #s>
NAF
As noted in a comment, its 4.7MΩ.
It's about 2x3 inches (50x75 mm).
In this case, the patent numbers are quite useful.
The first patent is on a liquid insulator/dielectric. That tends to point in the general direction of a capacitor, but not much more than that.
The second patent, however, is titled: "Electrical Capacitor". That seems to point pretty strongly toward it being an...electrical capacitor.
The third patent provides reasonable confirmation. It's titled "Paper suitable for capacitors, and process of making the same."
So, I'm going to go with "capacitor". The first patent covers a liquid dielectric. Given that it doesn't look like the liquid has leaked out, it seems fairly reasonable to guess that it's probably still even reasonably close to its original rating.
Yes, it is a capacitor. It could be a single-phase motor run capacitor, but a resistor is not typical for such capacitors. Since the series combination of the capacitor and the auxiliary motor winding is connected in parallel with the main motor winding, the capacitor will quickly discharge through the main winding when the power is disconnected making a discharge resistor unnecessary.
