Excerpts from the American Heritage dictionary:
NOUN 1. The fact or state of being possible. 2. Something that is possible. 3. possibilities Potentiality for favorable or interesting results: The idea has great possibilities.
4. A favorable set of circumstances; an opportunity: a chance to escape.
NOUN: Inflected forms: pl. op·por·tu·ni·ties
1a. A favorable or advantageous circumstance or combination of circumstances. b. A favorable or suitable occasion or time. 2. A chance for progress or advancement.
SYNONYMS: opportunity, occasion, opening, chance, break These nouns refer to a favorable or advantageous circumstance or combination of circumstances. Opportunity is an auspicious state of affairs or a suitable time: If you prepare yourself . . . you will be able to grasp opportunity for broader experience when it appears (Eleanor Roosevelt). Occasion suggests the proper time for action: an auspicious occasion; an occasion for celebration. An opening is an opportunity affording a good possibility of success: waited patiently for her opening, then exposed the report's inconsistency. Chance often implies an opportunity that arises through luck or accident: a chance for us to chat; no chance of losing. A break is an often sudden piece of luck, especially good luck: got his first big break in Hollywood.