Britain's Kate Middleton and her sister Pippa have bumped Lady Gaga off the international fashion map.

The wife of Prince William, now formally known as the Duchess of Cambridge, topped a fashion buzzword list for a second year running while outrageous pop star Lady Gaga disappeared from sight.

The Global Language Monitor, which tracks print, electronic and social media for top words and phrases, said on Wednesday that "The Duchess Effect" was its top fashion word for 2012. The proclamation comes as New York begins its fashion week of shows and celebrity parties.

Kate's sister, Pippa Middleton - who made waves as a bridesmaid at the Duchess's London wedding last year - also made the list.

"Pippa's bum" came in at No5, reflecting what the body said was the "absurdly large media interest in the duchess's sister in general and her bum in particular".

The duchess can sell out a fashion line in 24 hours just by wearing a dress or sweater from a retail store at a public event. Indeed, her style choices have influenced a more feminine look all round in fashion.

"The Duchess Effect appears to extend much further than the economic impact of Kate's fashion choices; this year the fashion landscape seems to be a brighter, more accessible place with the styles more colourful, feminine and graceful than we've seen in many years," said the Global Language Monitor's fashion expert, Bekka Payack.

It's the first time the same person has topped the group's annual fashion buzzword list for two years running.

Lady Gaga, whose outfits have ranged from a raw meat dress to one of black packing tape, was in second place last year and topped the list in 2010. But she failed to make the current line-up.

"The novelty [and shock value] of Lady Gaga's outrageousness has worn off.

"Entertainers such as Nicki Minaj, Kanye West and Katy Perry are also creating new personas with creative fashion choices - and setting new trends," Payack said.