Definitions of assure:

• verb:   assure somebody of the truth of something with the intention of giving the listener confidence

  Example: "I assured him that traveling to Cambodia was safe"

• verb:   inform positively and with certainty and confidence
• verb:   make a promise or commitment
• verb:   cause to feel sure; give reassurance to

  Example: "The airline tried to reassure the customers that the planes were safe"

• verb:   make certain of
• verb:   be careful or certain to do something; make certain of something