Patriot Day is a compound noun. "Patriot" acts as an attributive noun modifying "Day," collectively forming a specific name for an observance. Therefore, the phrase functions as a noun, specifically a proper noun, referring to a particular commemorative event.
Patriot Day is an annual observance in the United States, designated on September 11th of each year, to commemorate the nearly 3,000 victims who lost their lives in the terrorist attacks on September 11, 2001. The day also honors the first responders, emergency personnel, and military service members who bravely reacted to the events. It was established by a joint resolution of the U.S. Congress and signed into law by President George W. Bush on December 18, 2001. Although it is not a federal holiday, on Patriot Day, the President of the United States issues a proclamation, requesting that American flags be flown at half-staff at all U.S. government buildings, homes, and establishments, and that a moment of silence be observed at 8:46 a.m. Eastern Daylight Time, marking the time the first plane struck the North Tower of the World Trade Center.
The observance of Patriot Day serves as a solemn reminder of the profound impact of the 9/11 attacks on the nation. It fosters a collective moment of remembrance for those who perished, recognizes the enduring courage of those who responded, and encourages reflection on the themes of national unity, resilience, and vigilance against acts of terrorism. Communities across the country often hold memorial services, candlelight vigils, and acts of service to honor the fallen and reaffirm a commitment to peace and security.