PREP
(置于某个年份之前，表示不确定)大约，大概
Circa is used in front of a particular year to say that this is the approximate date when something happened or was made.
例句
The story tells of a runaway slave girl in Louisiana, circa 1850.
故事大约发生在1850年，讲的是路易斯安那州一个逃跑的年轻女奴。