There are several synonyms for the term "dark period" that can be used to describe a difficult or challenging time period. Some of these synonyms include "trying times", "rough patch", "low point", "turbulent era", "difficult phase", "time of hardship", and "period of adversity". Each of these synonyms can be used to describe a period of struggle and difficulty, whether it be in personal life or within a larger societal context. The use of these synonyms can add depth and nuance to writing, conveying a sense of empathy and understanding for those who may be going through a challenging time.