I looked up adversity in three different advanced learner's dictionaries and here are the results.
- Longman Dictionary of Contemporary English 5th Edition: "a situation in which you have a lot of problems that seem to be caused by bad luck"
- Cambridge Advanced Learner's Dictionary 4th Edition: "a difficult or unlucky situation or event"
- Oxford Advanced Learner's Dictionary 9th Edition: "a difficult or unpleasant situation"
Personally, I feel like the Cambridge and Oxford definitions are too vague and generic for the need for a word like adversity aside from more frequently occurring words such as difficulty or trouble, which can only bring about more tiresome "the-difference-between" questions. Based on the applications of the word in my textbook which are typically in the context of "being caused by bad luck" (born blind, involved in a plane crash, stuck in a snowstorm, etc.), I feel like the Longman definition should be the reliable one. What do you think?