The New Oxford American Dictionary has named "unfriend" - which means deleting a 'friend' on a social networking site such as Facebook - as its 2009 Word of the Year.

Oxford senior lexicographer Christine Lindberg said the word had both currency and potential longevity.

"In the online social networking context, its meaning is understood, so its adoption as a modern verb form makes this an interesting choice for Word of the Year.

She said most prefixed words beginning with 'un' were adjectives, such as 'unacceptable' or 'unpleasant'.

"There are certainly some familiar 'un-' verbs (uncap, unpack), but 'unfriend' is different from the norm.

"It assumes a verb sense of 'friend' that is really not used (at least not since maybe the 17th century!). Unfriend has real lex-appeal."

Richard MacManus, editor of Readwriteweb, said it was an odd choice given the growth of websites like Facebook.

"All the trends indicate there has been more social networking activity this past year - not less (as 'unfriend' implies). Facebook and Twitter have rocketed in popularity."

Social media consultant Simon Young also said he was surprised by the choice, as he didn't believe 'unfriending' was a significant part of social networking culture.

Recent words of the year have been mostly environment-related, including hypermiling (strategies to increase gas mileage such as removing roof racks or overinflating tyres, locavore (eating only locally produced food) and carbon neutral.

Mr Young said breaking the cycle by selecting a social media phrase could signal the start of a new trend.

"But I hope that goes together with environmentally friendly words into the public consciousness."

Other Word of the Year finalists
Hashtag - a # sign added to a word or phrase that enables Twitter users to search for tweets that contain similarly tagged items and view thematic sets

Intexticated - distracted because texting on a cellphone while driving a vehicle

Sexting - the sending of sexually explicit texts and pictures by cellphone

Freemium - a business model in which some basic services are provided for free, with the aim of enticing users to pay for additional, premium features or content

Funemployed - taking advantage of one's newly unemployed status to have fun or pursue other interests

Birther - a conspiracy theorist who challenges President Obama's US birth certificate

Teabagger - a person who protests President Obama's tax policies and stimulus package, often through local demonstrations known as "Tea Party" protests (in allusion to the Boston Tea Party of 1773).

Deleb - a dead celebrity

Tramp stamp - a tattoo on the lower back, usually on a woman