The day we all knew was coming has arrived. Twitter just added a subtle phrase to the right-hand side of every user's home page. That text? Sponsored definition. What that tells us is that Twitter has decided to start charging for companies to promote in the definition area that they added just a few weeks ago. The change was first noticed by Nimish Adani (Twitter) of workosaur.com.

We have written about Twitter courting revenue models like ExecTweets and suggested friends. However, it has kept its real monetization plans under wraps, content to move slowly, until now. It looks like the first applications to be highlighted as paying sponsors are Twitterrific, Tweetdeck and Stocktwits. We haven't seen any new changes to the business side of Twitter to indicate how advertisers would go about promoting their product on the site yet, but we're sure it is just a matter of time.

Update: It looks like we jumped the gun a bit: the official Twitter account just sent this tweet: "None of the promos currently running in the sidebar are sponsored (it just says that because of a bug that's being fixed right now)."

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