Facebook, which has gone after sites with the word "book" in their names, is also trying to trademark the word "face," according to court documents.

But the social networking site has met with a familiar foe. As TechCrunch first reported, Aaron Greenspan has asked for an extension of time to file an opposition to Facebook`s attempt. Greenspan is the president and CEO of Think Computer, the developer of a mobile payments app called FaceCash.

Greenspan, a former Harvard classmate of Facebook chief executive Mark Zuckerberg, claimed he had a hand in developing the social networking giant. The case was settled last year.

In an interview with CNNMoney.com, Greenspan said the two extensions he filed now give him until September 22 to oppose the "face" trademark attempt. The original deadline was June 23.

In the case of Teachbook, Facebook would have to prove the site caused "a likelihood of confusion," said Sneath, the trademark lawyer. That`s a steep burden, he said, but Facebook could succeed.

BDST: 1545 HRS, 30 August 2010