Soporific years refer to a period of time when someone is in a state of drowsiness or lethargy. There are several synonyms for this term that can be used to convey a similar meaning, such as sluggish years, lethargic years, somnolent years, sluggish phase, or laggard phase. These terms are often used to describe a period when one feels tired or unenergetic, and when they lack motivation or enthusiasm for daily activities. The use of synonyms can help writers to be more creative and expressive in their writing, allowing them to choose the best term to convey their intended meaning.