to say or write that something is true, correct etc

declare the truth of something

to give (legal) power to or right of control to (a person)

give power or control

to declare (usually by showing a certificate) that (something is true, correct)

declare as true

to state, show, the truth of (opinions, feelings etc)

ratify, validate, prove

to give support go certainty to (a statement, belief, theory etc)

back up information, story

to write one's name on the back of (a cheque)

support, authorize

to make (something) valid

ascertain the truth, authenticity of something

to be responsible for; express confidence, in a person, a person's character

give assurance