The two trains moved in opposite directions away from the station.

in opposite directions 是一个介词短语，其中 opposite 是形容词，意思是"相反的、对立的"，direction 是名词，意思是"方向"。 in opposite directions 字面意思是"在相反的方向上"，用来描述两个物体朝完全相反的方向移动。