天下
てんか · tenka · JLPT N1 · noun
universe
天 — 一 (one/sky) above 大 (big person)
Originally a pictograph of a person (大) with an emphasized head, representing what is above — the sky or heavens. The top stroke evolved into 一, symbolizing the vast expanse overhead. From 'sky' it extended to mean 'day,' 'heaven,' and 'nature.'
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'.