衍

• Physical/Natural: To overflow, spill over, or spread out; implies a gradual spreading or the widening of a river's reach. Can also imply lushness resulting from such overflow.
• Textual/Philological: Refers to "interpolated text" (衍文)—words or phrases that have entered a manuscript through copying errors or later additions; redundant, superfluous, or spurious.
• Technical/Abstract: To derive, expand, or develop further from a base point (e.g., expanding a formula).

• Verb: To overflow, spread, or proliferate.
• Adjective: Redundant, superfluous, expansive.
• Directionality: Movement is generally outward and forward, moving from a source toward a periphery.

• vs. 溢 (yì): While 溢 often suggests a sudden breach or a cup running over, 衍 typically implies gradual spreading or seeping. 溢 refers to the act of overflowing; 衍 refers to the state of having spread out.
• vs. 漫 (màn): Both involve spreading water, but 漫 often carries a sense of being unrestrained, haphazard, or random, whereas 衍 suggests a more natural extension of an existing source.

The primary meaning shifts significantly based on the genre of the text:

• In naturalistic or early descriptive texts, prioritize "overflowing," "spreading," or "lushness."
• In commentaries, philological treatises, or scholarly critiques, treat as a technical term for textual interpolation (superfluity).