To make known formally or officially. See Synonyms at announce. To state emphatically or authoritatively; affirm. To reveal or make manifest; show. To make a full statement of (dutiable goods, for example). Games To designate (a trump suit or no-trump) with the final bid of a hand in bridge. To make a declaration. To proclaim one's support, choice, opinion, or resolution. declare war To state formally the intention to carry on armed hostilities against. declare war To state one's intent to suppress or eradicate: declared war on drug dealing in the neighborhood.