宣言 (xuānyán) is a formal, weighty word for a public declaration or manifesto, often political or ideological. As a verb it means 'to proclaim' solemnly. It is more formal and grand than 宣布 (xuānbù, 'to announce') and 声明 (shēngmíng, 'to state'), which are used for everyday or official statements. 宣言 often implies a written document or a public stance.