Image copyright British Library Image caption A 19th-century watercolour by an unknown Indian artist depicts three Thugs strangling a traveller

In the wake of violence and unrest in Baltimore, media commentators as well as politicians - including President Barack Obama - called rioters "thugs", and were criticised for it. But the term has a much older history.

In the US, "thug" is a loaded term.

It's surfaced a lot in recent months, usually surrounding protests against the deaths of young black men in various American cities.

Activists and cultural critics have pointed out the term is often used to refer to black Americans, and white Americans doing similar things would not be labelled the same way.

And it's back in the news this week as rioters in Baltimore were tagged as "thugs." Even the city's African-American mayor, Stephanie Rawlings-Blake, used the term, though she softened her comments on Wednesday.

So it may be a surprise that the word originates far away, in India.

"As far as I can tell, thug goes back to the 14th Century," says Megan Garber, who traced the word's origin for a story in The Atlantic. "There was a gang of criminals known as the thuggee."

Garber says the Thugs were a huge criminal network that operated all around India's main roads.

"They would basically befriend travellers along the roads, gain the travellers' trust," she says. "And then they would murder them, usually by strangulation, and steal their valuables. It was all very violent."

Mark Twain was one of the first Americans to report on the group. Observations about the Thugs appeared in his book, Following the Equator: A Journey Around the World.

Published in 1897, the book started the steady rise of "thug" in popularity and usage in American English.

In the United Kingdom, the Thugs were much better known, thanks to British colonial rule in India.

Image caption A Google Ngram charting the frequency of the word "thug" in American English from 1800-2000

Prime Minister Margaret Thatcher used the word decades ago with relative frequency.

"Thugs" were everyone from unruly soccer fans to people involved in race riots.

Garber says the word thug actually rebounded in American popular culture, thanks in part to Indiana Jones and the Temple of Doom.

Image caption A Google Ngram charting the frequency of the word "thug" in British English from 1800-2000

"There was a plotline that involved kidnapping by way of thugs," she says. "A lot of Indian Americans actually protested the portrayal of the thugs in that movie, but that sort of brought it back into the cultural presence again."

Then hip-hop took the word. Tupac had it tattooed onto his body, and Cleveland's Bone Thugs-N-Harmony sent the word into cars and living rooms across the country.

In this conception of the word, Garber writes, thugs "are both victims and agents of injustice, they are both the products and producers of violence, and mayhem, and outrage".

She's also been listening to how people have been using the word in the Baltimore riots.

Image copyright Reuters Image caption More than 100 vehicles and 15 buildings were burned in the riots

"It's this very effective way of suggesting that the people who are doing the rioting and who are being called thugs don't actually have a right to their outrage," she says.

That's partly why there's widespread disgust in the African American community over its use. Just take the response Baltimore Councilman Carl Stokes gave to CNN's Erin Burnett over the word.

"It's not the right word to call our children 'thugs,'" Mr Stokes said. "These are children who have been set aside, marginalised, who have not been engaged by us."

"But how does that justify what they did?" Ms Burnett said. "That's a sense of right and wrong. They know it's wrong to steal and burn down a CVS and an old persons' home. I mean, come on."

"Come on? Just call them [n-word] . Just call them [n-word]," Mr Stokes said. "No, we don't have to call them by names such as that.

"You wouldn't call your child a thug if they should do something that would not be what you expect them to do."

Garber isn't surprised the word has become so loaded.

"In some sense, the history of language is about people trying to wield power over other people," she says.

"And so this is just one more example of that strife and that effort."

This story first appeared on the PRI's The World - a co-production of the BBC World Service, Public Radio International, and WGBH in Boston. Hear more at PRI.com/TheWorld.