Armenians -- and many others -- say there is no doubt that the World War I-era mass killings and deportations of up to 1.5 million Armenians in the eastern stretches of the Ottoman Empire constitute the 20th century's first genocide.
But 100 years later, using the term -- or refusing to do so -- comes with weighty political implications.
Turkey, whose modern borderlands include territories where Armenians once predominated, admits that there was large loss of life among the largely Christian group. But it says there was no orchestrated Ottoman effort to wipe out the empire's Christian minority -- and that the historical context was a brutal war where hundreds of thousands of Muslim Turks died as well.
Ankara recoils at the term "genocide" -- which is defined as a deliberate attempt to destroy a national, ethnic, racial, or religious group in whole or in part -- and typically lashes out when its foreign counterparts use it. When Pope Francis recently called the mass killings genocide, Turkey quickly recalled its ambassador to the Vatican.
With the 100th anniversary of the start of the massacres being marked on April 24, here's a rundown of the sometimes complicated terminology in common use.
At Least 22 Countries Call It Genocide
The list includes Armenia itself, Austria, Argentina, Belgium, Bolivia, Canada, Chile, Cyprus, France, Greece, Italy, Lebanon, Lithuania, the Netherlands, Poland, Russia, Slovakia, Sweden, Switzerland, Uruguay, Vatican City, and Venezuela.
The government in Germany, Turkey's largest European trading partner, has said it supports a draft parliamentary resolution that would for the first time link the killings to genocide.
The European Parliament voted to recognize the killings as genocide in 1987, and in April of this year, it angered Turkey by passing a nonbinding resolution calling on Ankara to do the same and to normalize ties with Armenia. Turkish President Recep Tayyip Erdogan said the vote would "go into one ear and out the other."
Four European Countries Outlaw 'Armenian Genocide' Denial…
...but enforcing it is hard.
Switzerland, Cyprus, Slovakia, and Greece have all approved laws similar to legislation against Holocaust denial, but in 2013 the European Court of Justice ruled that a Swiss court's decision to fine a visiting Turkish politician for calling claims of genocide an "international lie" violated his freedom of expression.
The court said that, unlike the Holocaust, which is a historical fact, there is a still a "contradictory debate" around the Armenian killings.
In 2012 France's Constitutional Court overturned a new law criminalizing "Armenian genocide" denial.
U.S. Says 'Great Calamity' But Not Genocide
As a U.S. presidential candidate, Barack Obama called the mass killings "genocide." But, like past presidents, his administration has so far refused to use the term, instead opting for the Armenian-language Meds Yeghern, or "great calamity."
Amid pressure from Turkey, the administrations of George W. Bush (in 2007) and Obama (in 2010) both successfully pressured the House of Representatives to avoid voting on proposals to recognize the World War I events as genocide.
UN Chief Says 'Atrocity Crimes'
Shortly after Pope Francis called the mass killings genocide, a spokesperson for UN Secretary-General Ban Ki-moon said that he considered the events "atrocity crimes."
The UN uses the term to describe "three legally defined international crimes: genocide, crimes against humanity, and war crimes."
The spokesperson, Stephane Dujarric, said Ban is "fully aware of the sensitivities related to the characterization of what happened in 1915."
A picture released by the Armenian Genocide Museum-Institute purportedly shows Armenians hung by Ottoman forces in Constantinople in June 1915.
Turkey Says 'Communal Violence'
The words katliam, which means massacre, and tehcir, meaning forced relocations, are frequently used in Turkey to describe the events of 1915. Mukatele, meaning mutual killings or communal violence, is also sometimes used by officials to imply culpability on all sides.
Article 301 of the Turkish Penal Code criminalizes insulting the "Turkish nation." In the past Turkish citizens have been prosecuted under the law for appearing to blame Turks for the mass killings, but in an April interview with Al Jazeera, Etyen Mahcupyan, a Turkish-Armenian adviser to Prime Minister Ahmet Davutoglu, said that there are no longer such cases.
Still, speaking publicly about the deaths can be dangerous. In 2007, a nationalist assassinated Hrant Dink, a Turkish-Armenian journalist who had written extensively about what he termed genocide. In 2008, 13 people were arrested in a plot to kill Nobel Prize-winning writer Orhan Pamuk, who had emphasized the Turkish role in the mass killings.
The Turkish word for genocide, soykirim, is used to describe other ethnic slaughters, including the Holocaust, the Rwandan genocide, and the massacre of Muslims by Bosnian Serbs at Srebrenica in 1995.
A picture released by the Armenian Genocide Museum-Institute, dated 1915, which purportedly shows soldiers standing over skulls of victims from the Armenian village of Sheyxalan in eastern Turkey during World War I.
Baku May Be Even More 'Antigenocide' Than Turkey
Azerbaijan and Armenia are bitter rivals who have been locked in a dispute over Nagorno-Karabakh for the past 20 years. The territory is internationally recognized as Azerbaijani but is controlled by ethnic Armenians.
The mass deaths of 1915 are rarely discussed in Azerbaijan. When officials use the term "genocide" in relation to the events of 100 years ago they typically precede it with a derisive adjective.
For instance, Deputy Prime Minister Ali Hasanov recently lashed out at the European Parliament's resolution, referring to the "fictional Armenian genocide."
New York Times Says Genocide, Other Media Don't
The New York Times reported extensively on the massacres of Armenians as they happened 100 years ago. At the time, the word "genocide" did not yet exist, but phrases like "Turks Accused Of Plan To Exterminate Whole Population" appear to fit with the modern definition of the term.
The paper now calls it a genocide and has done so regularly for the past 11 years.
Explaining his decision to The New Yorker in 2004, then-executive editor Bill Keller said, "I don't feel I'm particularly qualified to judge exactly what a precise functional definition of genocide is, but it seemed a no-brainer that killing a million people because they were Armenians fit the definition."
The Los Angeles Times and The Boston Globe also use the term. Other news organizations, including Reuters, the BBC, and RFE/RL's English-language website, stick to terms such as "mass killings" while describing the Armenian and Turkish positions.
Armenians Are Clear: This Was Genocide
Armenians have long battled for international recognition of what they say was clearly a genocide.
They frequently point to the words of Raphael Lemkin, the Polish-Jewish lawyer who fled to the United States during the Nazi invasion of Poland and is credited with coining the term.
"I became interested in genocide because it happened so many times," Lemkin said in a 1949 interview. "It happened to the Armenians, and after the Armenians Hitler took action."
WATCH: Raphael Lemkin On The Word 'Genocide'
News reports that Obama would refrain from using the word on the 100th anniversary of the mass killings sparked anger.
"We're outraged," Aram Hamparian, the executive director of the Armenian National Committee of America, told RFE/RL. "Essentially, what we've done as a country is we've outsourced our policy on the Armenian genocide to Recep Erdogan, the president of Turkey. We've allowed him, a foreign leader, to dictate to us what we can and can't say about this human rights issue."