isn't的完整形式：is not。is not（完全式）=isn't（缩写式）。
isn't（缩写式）= is not（完全式）
isn't
英[ˈɪznt]，美[ˈɪzənt]
例句
1、It isn't too difficult once you get the idea
你一旦弄懂了，就不太难了。
2、Perhaps he isn't coming.
他许不来了。
3、It's past the appointed time. Maybe he isn't coming.
约定的时间都过了，别是他不来了吧？
4、He is not my brother.=He isn't my brother.
