Twerking, the rump-busting up-and-down dance move long beloved on America's hip-hop scene, has officially gone mainstream. It has the English dictionary entry to prove it. Britain's Oxford Dictionaries said the rapid-fire gyrations employed by US pop starlet Miley Cyrus to bounce her way to the top of the charts had become increasingly visible in the past 12 months and would be added to its publications under the entry: "Twerk, verb." Although Cyrus' eye-popping moves at Monday's MTV Video Music Awards may have been many viewers' first introduction to the practice, Oxford Dictionaries' Katherine Connor Martin said "twerking" was some two decades old. "There are many theories about the origin of this word, and since it arose in oral use, we may never know the answer for sure," Martin said. "We think the most likely theory is that it is an alteration of work because that word has a history of being used in similar ways, with dancers being encouraged to 'work it'. The 't' could be a result of blending with another word such as twist or twitch." "Twerk" will be added to the dictionary as part of its quarterly update, which includes words such as "selfie", the word typically used to describe pouty smartphone self-portraits, "digital detox" for time spent way from Facebook and Twitter, and "Bitcoin", for the nationless electronic currency.