n. Dutch astronomer who calculated the size of the universe and suggested that it is expanding (1872-1934)
n. an organism (person or animal) that sits
n. a person engaged to care for children when the parents are not home
n. 临时照看孩子的人( sitter的复数形式 ); 不在飞行中或运动中的鸟或兽; 被画像或拍照的人; 容易命中的猎物