an一般用在元音字母前代替不定代词a，所以an后面可以加以元音字母开头的名词，比如：apple、umbrella、ice cream、Egg、orange、ant、elephant、hour、anima等。
an是一个英语单词，词性是限定词，释义为(指初次提及或非特指的人或物)一(个)；(一类人或事物中非特指的)任何一(个)；(用于前加形容词或后加修饰语的不可数名词之前)一(种)。
扩展资料：
与an有关的例句：
That clock's an hour fast.
那个钟快了一个小时。
My profession had an important influence in the formation of my character and temperament.
我的职业对我性格和脾气的形成有重要的影响。
He had been spotted by an alert neighbour.
一个警觉的邻居发现了他。
The cold war came to an end.
冷战结束了。
This man is an animal, a beast.
这人是个畜生，是个野兽。
He had been patiently waiting in the anteroom for an hour.
他在前厅耐心地等了一个小时。
I have an analytical approach to every survey.
对每项调查我都采用分析方法。
I fixed up an appointment to see her.
我安排了与她见面。
This has fuelled speculation that he is about to clinch a deal with an American engine. manufacturer.
这更增添了人们对他即将和美国的一家发动机制造商达成协议的猜测。
She has an appointment with her accountant.
她和她的会计约好了见面。
The summer came to an end.
夏天结束了。
参考资料来源：百度百科-an