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For Twitter’s nearly six million users, tweeting isn’t only for the birds.

The vast popularity of the micro-blogging site has the Oxford English Dictionary finally adding another definition to the word “tweet” in its dictionary.

Now, in addition to the melodic sounds that birds make, tweet can also mean “to make a posting on the social networking service Twitter,” and “to use Twitter regularly or habitually.”

“This breaks at least one … rule, namely that a new word needs to be current for ten years before consideration for inclusion,” notes chief editor John Simpson in a blog post.

"It seems to be catching on," he noted wryly.

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The dictionary’s inclusion of the word comes nearly two years after another version of the dictionary – the Concise Oxford English Dictionary – added the word “retweet” to its vast collection of words. Its competitor, the Merriam-Webster Collegiate Dictionary, added “tweet” to its dictionary in 2011.

Tweet, while new in the world of social media, is actually one of the oldest words. Its earliest recorded use was during the 16th century, according to the dictionary.

Other words – with roots in technology – were added to the Oxford English Dictionary, including mouseover and crowdsourcing.

The phrase, “Don’t have a cow” – popularized by the cartoon character Bart Simpson – was added as well. The humorous idiom has roots in the 1950s, according to the dictionary.