A city politician says he will no longer use the term "marijuana" because it is racist, sparking a social media debate over the common synonym for cannabis.

Shawn Cleary, a Halifax city councillor, says a police officer he works with on a cannabis legalization task force recently brought to his attention that the term has a racist history.

Mr. Cleary said in the early 1900s, during the criminalization of cannabis in the United States, "marijuana" was used to demonize marginalized communities, namely Mexicans.

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He said after doing some of his own research on the term's origins, he decided to stop using it, saying earlier this week on Twitter: "Let's do what we can to not perpetuate racism."

In an interview on Thursday, Mr. Cleary said, "We need to actually have conversations, have dialogue, and talk about these things. By doing that we're actually increasing the amount of understanding and interest in history.

"These are teaching moments. They are opportunities for us to go and learn stuff and to find out more about the history of the world around us."

His tweets have prompted a social media firestorm – including comments from a fellow councillor denouncing the issue.

"Only in Canada could you smoke it but not say it," Matt Whitman said on Twitter in response to a poll from a local Halifax radio station that asked on Twitter: "Should we stop using the word marijuana?"

Some Twitter users said they were unaware of the word's racist history and thanked Mr. Cleary for informing them, while others questioned the validity of his comments.

Earlier this year, the U.S. National Hispanic Caucus of State Legislators passed a resolution calling for the decriminalization of cannabis, and took note of its racist history.

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"During the 1920s and 1930s, when it was first penalized in various states, cannabis use was portrayed as a cultural vice of Mexican immigrants to the United States, and racist and xenophobic politicians and government officials used cannabis prohibition specifically to target and criminalize Mexican-American culture and incarcerate Mexican-Americans," the document said.

"The racist politicians who first criminalized cannabis, used the term "marijuana" … to refer to it, precisely because they wanted to underscore that it was a Latino, particularly Mexican 'vice.'"

Barinder Rasode, CEO of the National Institute for Cannabis Health and Education, said cannabis is a more "progressive" term and one that should be used as the country moves toward legalization next July.

"We've seen words that are used to describe ethnic communities, sexual orientation and women have changed over time because we're recognizing issues of equality and progressiveness," Ms. Rasode said.

"I do believe the word marijuana has context attached to it of the old world – the illegal market. When I grew up, cannabis was considered a gateway drug. Now, as our understanding has changed and considering the role the product will now play in society, I think with that we do have to change words because marijuana has negative connotations."