上shàng means up, on top of and above, e.g. 上shàng 午wŭ above the noon. Therefore it is ‘morning‘.
下xià means down, under and below, e.g.下xià 午wŭ below the noon. Therefore, it is ‘afternoon‘.
Both of them can be verbs too, which mean (1) ascend and descend respectively, 上shàng 山shān going up to the mountain and 下xià 山shān going down the mountain; 上shàng 楼lóu going up stairs and 下xià 楼lóu going down stairs, for example. However, 楼lóu 上shàng is upstairs and 楼lóu 下xià is downstairs. (more…)