Reference > Brewer’s Dictionary > Arras,  tapestry. So called
from Arras, in Artois, famed for its manufacture. When rooms
were hung with tapestry it was a common thing for persons to
hide behind it, especially the arras curtain before the door.
Hubert concealed the two villains who were to put out Arthur’s
eyes behind the arras. Polo’nius was slain by Hamlet while
concealed behind the arras. Falstaff proposed to hide behind the
arras at Windsor, etc.   1