1.number1
2.used in formal language or for emphasis before hundred,thousand,ect.or before a unit of measurement(正是用语或表示强调，用在hundred、thousand等或度量单位之前)一。
3.used for emphasis to mean ‘a single' or 'just one'(表强调)单独一个，仅仅。
4.a peason or thing,especially when they are part of a group(尤指一组中的)一个人，一件事物。
5.used for emphasis to mean'the only one'or'the most important one'(表强调)只有一个的，最重要的一个。
6.used when you are talking about a time in the past or the future, without actually saying which one(用于一般地谈论过去或将来的某个时间)
7.the same 同一个。
8.(informal,especially NamE)used for emphasis instead of a or an(代替a或an,表示强调)。
