testify

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive verb To give testimony in a legal case or before a deliberative body.
• intransitive verb To express or declare a strong belief, especially to make a declaration of faith.
• intransitive verb To make a statement based on personal knowledge in support of an asserted fact; bear witness.
• intransitive verb To serve as evidence.
• intransitive verb To declare publicly; make known.
• intransitive verb To state or affirm as testimony in a legal case or before a deliberative body.
• intransitive verb To be evidence of.

from The Century Dictionary.

• To bear witness; make declaration, especially for the purpose of communicating to others a knowledge of some matter not known to them, or for the purpose of establishing some fact.
• In law, to give testimony, under oath or solemn affirmation, in a cause depending before a court.
• To serve as evidence; be testimony or proof.
• To bear witness to; affirm or declare as fact or truth.
• In law, to state or declare under oath or affirmation, as a witness, before a tribunal.
• To give evidence of; evince; demonstrate; show.
• To make known; publish or declare freely.

from the GNU version of the Collaborative International Dictionary of English.

• intransitive verb To make a solemn declaration, verbal or written, to establish some fact; to give testimony for the purpose of communicating to others a knowledge of something not known to them.
• intransitive verb (Law) To make a solemn declaration under oath or affirmation, for the purpose of establishing, or making proof of, some fact to a court; to give testimony in a cause depending before a tribunal.
• intransitive verb To declare a charge; to protest; to give information; to bear witness; -- with against.
• adverb In a testy manner; fretfully; peevishly; with petulance.
• transitive verb To bear witness to; to support the truth of by testimony; to affirm or declare solemny.
• transitive verb (Law) To affirm or declare under oath or affirmation before a tribunal, in order to prove some fact.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb to make a declaration, or give evidence, under oath
• verb to make a statement based on personal knowledge or faith

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb give testimony in a court of law
• verb provide evidence for