上下
じょうげ · jouge · JLPT N2 · noun
low
🛗 上 up + 下 down = 上下: two opposites combined into one word for the full range
上 is a short stroke with a mark above it, and 下 is the same stroke with the mark below. Together they name the whole span from high to low.
上 — horizontal line above a baseline
上 is an indicative character (指事): a short stroke placed above a longer reference line shows the concept of 'above' or 'up'. The earliest oracle-bone forms used two horizontal lines for this; the modern shape added a vertical stroke for clarity. The core meaning of 'upper, above, to ascend' has stayed stable for millennia.
下 — horizontal line 一 + mark below
下 is an indicative character: a long horizontal line represents a reference level, and a shorter stroke placed beneath it points to the area below. The original meaning 'below, down' comes directly from this spatial diagram, and it later extended to verbs like 'descend' and 'lower'.