Seit is a German word that means "since" or "for." It can be used in various contexts, including time-related phrases such as "seit Jahren" (for years) and "seit gestern" (since yesterday). There are several synonyms for the word seit that can be used interchangeably in different situations. Examples include "seither," "von da an," "ab," "dann," and "daraufhin." These words all convey the same idea of a specific period of time passing since an event occurred. The appropriate synonym to use depends on the context of the sentence and the tone intended.