Definition of "testify" []

• To make a declaration of truth or fact under oath; submit testimony: witnesses testifying before a grand jury. (verb-intransitive)
• To express or declare a strong belief, especially to make a declaration of faith. (verb-intransitive)
• To make a statement based on personal knowledge in support of an asserted fact; bear witness: the exhilaration of weightlessness, to which many astronauts have testified. (verb-intransitive)
• To serve as evidence: wreckage that testifies to the ferocity of the storm. (verb-intransitive)
• To declare publicly; make known: testifying their faith. (verb-transitive)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Having Cheney testify is truly pointless – he's made a career of lying and seems to be quite good at it."
• "That, as many ex-girlfriends of mine will testify, is quite untrue."
• "At an inquiry into the tasering death of amentally ill man in Nova Scotia, aclin­ical psychol­o­gist who has been called to testify is taking on the concept of “excited delirium”."