Word.

My favorite word is "word." This has been so for a very long time. I use the word "word" very often. "Word" is a great word. It works on so many levels.

To be in agreement with a statement:
"Those shoes are hideous."
"Word."

To answer “yes” to a question:
"Are familiar with the quadratic equation?"
"Word."

To express delight:
"My parents died, but they left me a buttload of cash!"
"Word!"

To be used as a question after a statement, in the place of "Really?":
"I just cured cancer!"
"Word?"

The common meaning:
"A word is a unit of language that carries meaning and consists of one or more morphemes which are linked more or less tightly together, and has a phonetic value."

And, finally, the Microsoft word processing program, Word:
"Dude, Word sucks."
"Word."

WORD.