To proclaim means to announce something publicly and officially, often something important or ceremonial. When a mayor proclaims a day of celebration for the town, she's making a formal, public declaration that everyone should know about. When a teacher proclaims the winner of the spelling bee, she's announcing it clearly and authoritatively so the whole class hears.

The word carries weight and formality. You wouldn't proclaim that you're having pizza for dinner: you'd just say it. But a president might proclaim a national day of remembrance, or a king might proclaim a new law throughout his kingdom. The word suggests speaking loudly, clearly, and with authority, making sure your message reaches everyone who should hear it.

Sometimes people use proclaim when someone states their beliefs or opinions very strongly and publicly. A scientist might proclaim her findings at a major conference. An inventor might proclaim that his new device will change the world. In these cases, the person is declaring something confidently and publicly, wanting others to take notice and pay attention.

A proclamation is the official announcement itself, like the Emancipation Proclamation, which declared enslaved people in rebel states to be free.