adj.三层的；三重的；三股的
n.三重；三股；三层夹板
Their wedding cake had three tiers. 他们的结婚蛋糕是三层的。
This is a rope of three strands. 这是一条三股的绳子。
Biodegradation has at least three definitions. 生物降解至少有三重含义。
