详细解释:n. 回归线
英语解释：
名词 tropic:
either of two parallels of latitude about 23.5 degrees north and south of the equator representing the points farthest north and south at which the sun can shine directly overhead and constituting the boundaries of the Torrid Zone or tropics形容词 tropic:
relating to or situated in or characteristic of the tropics (the region on either side of the equator)同义词：tropical