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3.
1. Slang term for a vulgar word because most of the most vulgar words are four letters long. All of George Carlin's Seven Dirty words are either four letters long, or contain a vulgar four letter word.

2. Any word, that while not vulgar, may have unpleasant connotations to the person referring to it as such.
1. Bob got fired from his job because he said a four letter word to a customer

2. Love is a four letter word
by Ycarus December 20, 2008
 
1.
Phrase that refers to any number of "bad" words, often seen in forum posts. Can mean shit, fuck, damn, and even other non-four-lettered-words such as ass and bitch. Can also refer to the basic four letter words with suffixes (ie "ed" "ing"). Usually said by some religious freak or ten year old that will get in trouble if their parents see it.
Poster 1
Damn man, that shit is fucking awesome! That bitch totally deserved it!

Poster 2
I could've understood what you were saying without all the four letter words...

<flame war against poster 2 ensues>
by Metatag October 12, 2005
 
2.
Another name for a swear word, which commonly, but not necessarily needs to consists of four letters.
Person A: Hey, i saw this guy yesterday and he said 'hi', then i said 'hey' and we started a conversation.
Person B: That was me you fucking moron!
Person A: Ok ok, no need for the four letter words.
Person b: Huh?..........."That"????
by Blackington September 11, 2006
 
4.
A set of words written with four letters that are considered obscene or vulgar unless written on the internet.
four-letter words in Real Life:
Kid - "shit..."
Dad - "What the Fuck did you say?"
On the Net:
Kid - "omg slut. damn what a fucking shit cunt"
Dad - "qft"
by Kirkface September 25, 2005