state emphatically and authoritatively
"He declared that he needed more money to carry out the task he was charged with"
designate (a trump suit or no-trump) with the final bid of a hand
"After winning the bidding, she declared hearts as her trump suit."
make a declaration (of dutiable goods) to a customs official
"Do you have anything to declare?"
proclaim one's support, sympathy, or opinion for or against
"His wife declared at once for moving to the West Coast"
To make clear, explain, interpret.
"The judge declared that the contract was void because it lacked essential terms."
In plain English: To declare means to say something out loud so that everyone knows it is true.
"The captain declared that their flight was delayed due to bad weather."
From Middle English declaren, from Old French declarer, from Latin dēclārō ("to make clear"), from dē- + clārus ("clear").