As other answerers have pointed out, thug traces its origin to a cult in India. But of course how people use it in the modern day isn't bound by its past associations. In film noir, thug was commonly used interchangeably with goon, and referred to gangsters who provided the brute force for a protection racket or other criminal enterprise.

To find a connection specifically between thug and with real or imagined African-American outlaw behavior, I think you have to look to the evolution of gangsta rap. In the 1980s, gangsta rap emerged from so-called "hardcore hiphop," and the term gangsta became specifically associated with black gangs and organized criminals. In 1992–1993, two influential groups appeared that adopted thug in their post-gangsta self-description: Thug Life (whose most famous member was Tupac Shakur) and Bone Thugs-n-Harmony (a Cleveland group whose first big hit was "Thuggish Ruggish Bone" and whose first EP for Ruthless Records was, according to the Wikipedia article about the group "focused almost entirely on violent criminal activity").

The Urban Dictionary has an interesting definition posted by a user, widely approved by its voting members:

As Tupac defined it, a thug is someone who is going through struggles, has gone through struggles, and continues to live day by day with nothing for them. That person is a thug. and the life they are living is the thug life. A thug is NOT a gangster. Look up gangster and gangsta. Not even CLOSE, my friend.

From the sound of it, Tupac Shakur defined thug much the way an earlier generation of African-Americans might have defined ghetto—dangerous, hardened by struggles, and living on the edge due to an extremely hostile environment. But what he and his fans might have in mind by thug isn't necessarily what people outside his milieu might make of it. And in the non-hiphop precincts of the United States, it seems safe to say, thug is not used sympathetically.

I don't know how widespread the association of thug with African-Americans is in U.S. culture; until now I hadn't thought of the two as particularly connected. But code words (where speakers signal a racial or ethnic identity without overtly spelling it out) have a long history in English and probably many other languages, and I wouldn't be surprised if at least some people use thug pejoratively to refer to specifically African-American people who behave in an aggressive or otherwise scary way.

As other answerers have pointed out, thug traces its origin to a cult in India. But of course how people use it in the modern day isn't bound by its past associations. In film noir, thug was commonly used interchangeably with goon, and referred to gangsters who provided the brute force for a protection racket or other criminal enterprise.

To find a connection between thug and real or imagined African-American outlaw behavior, I think you have to look to the evolution of gangsta rap. In the 1980s, gangsta rap emerged from so-called "hardcore hiphop," and the term gangsta became specifically associated with black gangs and organized criminals. In 1992–1993, two influential groups appeared that adopted thug in their post-gangsta self-description: Thug Life (whose most famous member was Tupac Shakur) and Bone Thugs-n-Harmony (a Cleveland group whose first big hit was "Thuggish Ruggish Bone" and whose first EP for Ruthless Records was, according to the Wikipedia article about the group "focused almost entirely on violent criminal activity").

The Urban Dictionary has an interesting definition posted by a user, widely approved by its voting members:

As Tupac defined it, a thug is someone who is going through struggles, has gone through struggles, and continues to live day by day with nothing for them. That person is a thug. and the life they are living is the thug life. A thug is NOT a gangster. Look up gangster and gangsta. Not even CLOSE, my friend.

From the sound of it, Tupac Shakur defined thug much the way an earlier generation of African-Americans might have defined ghetto—dangerous, hardened by struggles, and living on the edge due to an extremely hostile environment. But what he and his fans might have in mind by thug isn't necessarily what people outside his milieu might make of it. And in the non-hiphop precincts of the United States, it seems safe to say, thug is not used sympathetically.

I don't know how widespread the association of thug with African-Americans is in U.S. culture; until now I hadn't thought of the two as particularly connected. But code words (where speakers signal a racial or ethnic identity without overtly spelling it out) have a long history in English and probably many other languages, and I wouldn't be surprised if at least some people use thug pejoratively to refer to specifically African-American people who behave in an aggressive or otherwise scary way.