Sentence:  A decade ago most psychiatrists would have been puzzled to find a chapter on <WSD>dysthymia</WSD> in a book about severe depressive disorders. They would have characterized this chronic form of depression as mild, "minor," or "syndromal."...In recent years, research has demonstrated the severity, prevalence, and importance of vogorous antidepressant treatment of <WSD>dysthymia</WSD>, justifying its inclusion here among serious mood disorders. 
Meaning of the word marked with <WSD> tags:  A form of clinical depression, characterized by low-grade depression which lasts at least 2 years.