The climbers began their slow descent down the steep mountain slope.

descent 是名词，来自动词 descend（下降、下坡）。de- 是前缀表示"向下"，scend 来自拉丁词根 scandere 表示"爬"。所以 descent 字面意思是"向下爬"，引申为"下降、下坡"的过程或路径。