verb · extending or spreading out continuously, often used in describing scenes or processions that seem to lengthen or propagate in a rhythmic, continuous way.

这古代祭祀仪式的场面曼衍，气势宏大。

to spread out, develop, or evolve over time

许多现代汉语词汇都是由古汉语衍生而来的。

verb · to flow over, flood, or inundate

水满而衍，流于平地。

redundant or unnecessary, especially in the context of extra characters in a text

这段文字中多出了一个字，应该是衍文。