The rally was poignantly staged in front of the statue of Alexander the Great.
Athens argues that the use of the term "Macedonia" suggests the former Yugoslav state has territorial claims to a northern Greek region of the same name. "It is impressive", rally organiser Anastasios Porgialidis told AFP.
The rally is part of a 27-year disagreement between the Greek province of Macedonia, of which Thessaloniki is the capital, and the country of Macedonia.
Thousands of Greeks flooded into the city of Thessaloniki today to protest against a United Nations plan that could finally put an end one of the world's most weird but emotive disputes: what to call Macedonia.
Greece has blocked attempts by Macedonia to join North Atlantic Treaty Organisation and the European Union.
Death toll from Montecito mudslides at 21 after missing mother located
Authorities said a search and recovery dog team located the body of an adult woman around 10 a.m., CBS Los Angeles reports. Crews worked around the clock clearing drainage areas, stabilizing embankments and repairing guardrails and signs.
The issue has been a source of conflict between the two countries ever since Macedonia's independence from Yugoslavia in 1991.
At the protest, far-right leaders, Greek diaspora groups and clerics called against any UN-sponsored compromise name for their northern neighbor that would include the term "Macedonia". "This is not negotiable", said Leonardou, a 59-year-old writer from Thessaloniki, warning that if the Greek government does otherwise "there will be an answer from the Greek people".
Protesters carried Greek flags and banners saying "Macedonia is Greek" and sang the Greek national anthem and the anthem of Greek Macedonia and chanting the slogan "There is only one Macedonia and it is Greek". Leaked reports of the solutions being discussed led to vehement speculation and no shortage of nationalist rhetoric in Greece.
Tsipras, who is expected to meet with his Macedonian counterpart Zoran Zaev in Davos next week, said in an interview published on Sunday: "If there is an opportunity for a solution, it would be a national stupidity not to make good use of it".
However, he told Ethnos newspaper that he could understand "the concerns and sensitivities" of Greeks in the region of Macedonia. United Nations envoy Matthew Nimetz is said to have put five proposals on the table: the two mentioned above as well as Republika Gorna Makedonija (Republic of Upper Macedonia), Republika Severna Makedonija (Republic of Northern Macedonia) and Republika Makedonija [Skopje] (Republic of Macedonia [Skopje]).