Occasion and opportunity both mean "chance" and can be used interchangeably in some circumstances. For instance : You'll have an opportunity to meet her. You'll have occasion to meet her. In that example using "opportunity" is more informal. Occasion has another meaning, though. It refers to an event, an experience or incident. For example: On that occasion everyone was in a good mood. If you used "opportunity" in that sentence it wouldn't make any sense.

Opportunity is an appropriate or favorable time or occasion which results in a situation or condition favorable for attainment of a goal. e.g Their meeting afforded an opportunity to exchange views. Occasion is a particular time, especially as marked by certain circumstances or occurrences. e.g They met on three occasions to discuss the plan. Occasion is also a special or important time, event, ceremony, celebration, e.g His birthday will be quite an occasion and an opportunity for the family to meet. Occasion can be a convenient or favorable time, resulting in an opportunity, or situation. e.g This slack period would be a good occasion to take inventory.

www.the freedictionary.com/opportunity www.the freedictionary.com/occasion

An opportunity is something similar to a chance. You can give another person a chance or an opportunity. An occasion is a situation or circumstances that just happens. You can't give another person an occasion.

Opportunity means a chance that is beneficial to you. eg: I want an opportunity to prove my skills. Occasion means a situation , it can be a function or a ceremony etc. eg: On the occasion of my birthday, I invited all my friends to the party. Hope this helps :) :)