Definitions of vouch:

• verb:   give supporting evidence

  Example: "He vouched his words by his deeds"

• verb:   summon (a vouchee) into court to warrant or defend a title
• verb:   give personal assurance; guarantee

  Example: "Will he vouch for me?"

• verb:   give surety or assume responsibility

  Example: "I vouch for the quality of my products"