First, make sure that you have the Lynx web browser:
sudo apt-get install lynx
Now, make the following script:
#!/bin/sh
lynx -dump "http://wordnet.princeton.edu/perl/webwn?s=$1" | grep -B 1000 References | grep -A 1000 relations | less
Now you can define any word from the terminal. For example, suppose I want to know the definition of ‘psychoanalysis’, I can simply run:
./define psychoanalysis
and get the definition printed out.
It’s nothing fancy; just grabs the output from an online dictionary and spits it out to the terminal, but I find it to be very useful.