to ascertain the truth, accuracy, or reality of (something)
to bear out, confirm, or fulfil (something)
You see how this House of Commons has begun to verify all the ill prophecies that were made of it — Coleridge
to substantiate (something) in law, esp formally or on oath
verifiable adj
verification noun
verifier noun
[Middle English verifien via French from medieval Latin verificare, from Latin verus true]