What does "curtain" mean?

Additional senses

1. 2.(Arch.) That part of a wall of a building which is between two pavilions, towers, etc.
2. 3.A flag; an ensign; -- in contempt. [Obs.] Shak. Behind the curtain, in concealment; in secret. -- Curtain lecture, a querulous lecture given by a wife to her husband within the bed curtains, or in bed. Jerrold. A curtain lecture is worth all the sermons in the world for teaching the virtues of patience and long-suffering. W. Irving. -- The curtain falls, the performance closes. -- The curtain rises, the performance begins. -- To draw the curtain, to close ot over an object, or to remove it; hence: (a) To hide or to disclose an object. (b) To commence or close a performance. -- To drop the curtain, to end the tale, or close the performance.
3. 4.To inclose as with curtains; to furnish with curtains. So when the sun in bed Curtained with cloudy red. Milton.