Definitions of occasion:

• noun:   reason

  Example: "There was no occasion for complaint"

• noun:   an opportunity to do something

  Example: "There was never an occasion for her to demonstrate her skill"

• noun:   the time of a particular event

  Example: "On the occasion of his 60th birthday"

• noun:   an event that occurs at a critical time

  Example: "It was needed only on special occasions"

• noun:   a vaguely specified social event

  Example: "An occasion arranged to honor the president"

• verb:   give occasion to