A joss is a figure (made of porcelain, wood, or other material) of a Chinese god or deity that is worshipped, sometimes in a shrine.
What is a joss (from Victory, by Joseph Conrad)?
In Victory, Captain Davidson relates his experience in returning the shawl to Mrs. Schomberg. He finds it almost impossible to believe that this inane and apparently senseless woman is in reality an expert at hiding her true feelings:
As to Mrs. Schomberg, she sat there like a joss. Davidson was lost in admiration. He believed, now, that the woman had been putting it on for years. She never even winked. It was immense! The insight he had obtained almost frightened him; he couldn't get over his wonder at knowing more of the real Mrs. Schomberg than anybody in the Islands. . .