Vouch (verb)

1. To give personal assurance or guarantee.
2. To provide evidence or testimony in support of something.
3. To back or support something, someone.

Origin:

From middle english vouchen, from old english gefēcan "to assure".

Examples:

1. I can vouch for his integrity.
2. He vouched for the authenticity of the document.
3. I'll vouch for you, so you can borrow the money from the bank.
4. The witness vouched for the defendant's alibi.
5. I vouched for him and he got the job.