昃

The core sense is the process of the sun tipping or slanting toward the west after reaching its zenith. Literally, it denotes the period from noon until sunset, emphasizing the angle of light and the movement of descent. Metaphorically, it refers to any state of waning or inevitable decline, such as the fading of power, the end of a dynasty, or the later stages of human life.

Can function as a verb (to decline; to slant; to pass the meridian) or as a noun/adjective (the afternoon; the period of descending light).

Distinguish from other terms for the end of the day:

• 昃 vs. 夕 (xī): 昃 is the process of declining; 夕 is the result (evening/nightfall).
• 昃 vs. 暮 (mù): 昃 refers specifically to the sun's position and angle; 暮 refers to dusk or the closing of the day.
• 昃 vs. 沒 (mò): 昃 is the slanting descent; 沒 is the actual disappearance below the horizon.

In poetic, philosophical, or political contexts, "afternoon" may be too domestic a term. Depending on the register, consider "waning," "declining," or "passing the meridian."