"Word" comes from the english saying "my word" which in turn comes from "I give you my word". Meaning that a statement is right and you would be willing to put your honor on the line to back it up.
Once again, this comes from "my word". When one says "word" as if asking a question, he or she is asking if the person that made the statement would swear to it.
Example 1:
Person 1: "Man having chapped lips is annoying."
Person 2: "Word." (meaning I agree and I would swear to it)
What usually occurs on urbandictionary.com when morons don't understand how to use brackets in the proper manner. I mean, I'm reading the instructions right now and it's easy shit. How can these morons fuck that up!?!?!
Jimmy posted a definition on here and wanted to link it to other words to better help the reader understand his definition. Unfortunately, he's a fuck up and put word all over the place instead of simply placing brackets around the word he wanted to link. Idiot.