[, ] () the period of time that you can use an asset such as a machine or a vehicle before it is worth buying a new one to replace it可用年限；使用寿命◆This machinery has an estimated useful life of 80 000 running hours.这台机械的预计使用寿命为 8 万运转小时。SYNeconomic life ⓘ An asset is depreciated (reduced in value) over its useful life.资产在其可用年限内逐步折旧（depreciate）。