WordNet: Princeton 大学的心理学家，语言学家和计算机工程师联合设计的一种基于认知语言学的英语词典。它不是光把单词以字母顺序排列，而且按照单词的意义组成一个“单词的网络”。

比如，如果查一个单词: train. 我们马上可以得到它的6个名词词意和11个动词词意，这些叫做"sense"。

1. (24) train, railroad train -- (public transport provided by a line
of railway cars coupled together and drawn by a locomotive; "express
trains don't stop at Princeton Junction")
2. (1) string, train -- (a sequentially ordered set of things or
events or ideas in which each successive
member is related to the preceding; "a string
of islands"; "train of mourners"; "a train of thought")
....

我们于是可以问 WordNet：“train 属于一种什么类型的东西？” 它回答：

Sense 1
train, railroad train
=> public transport
=> conveyance, transport
=> instrumentality, instrumentation
.....
Sense 2
.....

你就知道 train 是一种 public transport, 而public transport是一种 transport, 而transport又是 一种instrumentation.

你还可以问：“train 包括那些部分？” WordNet 回答：

Sense 1
train, railroad train 
HAS MEMBER: car, railcar, railway car, railroad car 
HAS MEMBER: locomotive, engine, locomotive engine, railway locomotive 
...
Sence2
...

嗯。火车包含车厢(car)，火车头(locomotive)，发动机……。你是不是学到了很多？呵呵。

再来看看，我问：“有哪些类型的train?” WordNet 回答：

Sense 1
train, railroad train 
=> boat train 
=> car train 
=> freight train, rattler 
=> hospital train 
=> mail train 
=> passenger train 
=> streamliner 
=> subway train 

再问：“跟 train 属于同一类的还有哪些东西？”

Sense 1
train, railroad train 
-> public transport 
=> bus, autobus, coach, charabanc, double-decker, 
jitney, motorbus, motorcoach, omnibus 
=> deadhead 
=> express 
=> local 
=> shuttle 
=> train, railroad train 

对呀。train 是一种公共交通工具，公共交通工具还有bus, deadhead, ...

嘿嘿！deadhead 是什么呢？来看看：

1. (1) deadhead -- (a nonenterprising person who is not paying his
way; "the deadheads on the payroll should be eased out as fast as
possible")
2. deadhead -- (a train or bus or taxi traveling empty)

嗯。空车。还有一个意思：白搭车的人？……我们来看看跟白搭车的人一类的人还有哪些：

Sense 1
deadhead 
-> nonworker 
=> deadhead 
=> idler, loafer, do-nothing, layabout, bum 
=> retiree, retired person 
=> striker 
=> unemployed person 
=> vacationer, vacationist 

这些都是不干活的人，嗯…… 不做事的，退休的，罢工的，失业的，放假的……

train 还有动词的含义，我们来看其中一个：训练。

1. (14) train, develop, prepare, educate -- (create by training and
teaching; "The old master is training world-class violinists"; "we
develop the leaders for the future")

这是主动动作，看例句就知道了。来看看，有哪些种类的训练？

Sense 1
train, develop, prepare, educate 
=> retrain 
=> drill 
=> housebreak 
=> toilet-train 

哦~ 教人新东西，军事训练，教你的宠物怎样干净的在屋里生活(这个很重要哟: P)，教你的小孩子怎样使用厕所……嗯……

你是不是发出一声惊叹！这个东西太神奇了！还有一个好消息就是：这个神奇的东西居然不要钱！好了。到 WordNet 的网站去下载这个程序吧 :)

给你一个抓图看看。