Both opportunity and possibility mean that there is a chance for something achievable, to succeed in something. However, they can not be used as synonyms for each other in any situations. Opportunity refers to something being possible for you to do because the circumstances are favorable or ucky at the time. In other words, it is an appropriate time or occasion and comes with some defined realities. Possibility, on the other hand, means the fact that something might happen or be true. Also, it is used with of or that. It has fewer assurances.
