(元音前用an) ［called the indefinite article］
1
- used when mentioning someone or something for the first time in a text or conversation用于第一次提及某人或某事物有个, 某个, 一个：
a man came out of the room
一个男人走出了房间
it has been an honour to have you
你能来真是荣幸
we need people with a knowledge of languages.
我们需要有语言知识的人。比较THE.
1.1
- used with units of measurement to mean one such unit［与度量单位连用, 表示一个单位］一：
a hundred
一百
a quarter of an hour
一刻钟。
1.2
- with negative one single; any一个; 任何一个：
I simply haven't a thing to wear.
我简直没有衣服可穿。
1.3
- used when mentioning the name of someone not known to the speaker用于提及说话者不认识的人某一个：
a Mr Smith telephoned.
有个史密斯先生打电话来过。
1.4
- someone like (the name specified)［与具体人名连用］像…的人：
you're no better than a Hitler.
你就像个希特勒。
2
- used to indicate membership of a class of people or things用于表示某一类人或事物一个, 一：
he is a lawyer
他是律师
this car is a BMW.
这是辆宝马车。
3
- in, to, or for each; per (used when expressing rates or ratios)用于表示速度或比率每：
typing 60 words a minute
每分钟打60个词
a move to raise petrol prices by 3p a litre.
将汽油价格每升提高三便士的动议。
USAGE
On the question of using a or an before words beginning with h, see usage at AN.
词源
Middle English: weak form of Old English ān'one'.
1.1
- (in travel timetables) arrives.用于旅行时刻表同arrives:
Penzance a 0915.
9点15分到达彭赞斯。
1.2
- in combination(in units of measurement) atto- (10-18).（度量单位）同ATTO-.
1.3
- Brit. (with reference to sporting fixtures) away.〈英〉（比赛的安排）同AWAY:
March 15 Sheffield United (a)
谢菲尔德联队将于3月15日在客场举行比赛。
1.4
- (used before a date) before在…之前（用于日期之前）：
a1200.
1200年前。
ORIGIN: from Latin ante.
- Physics acceleration【物理】加速度。