複合
ふくごう · fukugou · JLPT N1 · noun
complex
複 (fuku, multiple) + 合 (gou, combine): many parts joined together
Compound words in Japanese: 複 means duplicate or multiple, 合 means join or fit together. Something made of several joined parts is 複合.
合 — 乛 (lid/roof) + 口 (mouth)
Originally a pictograph of a lidded vessel — a cover (亼) closing over an opening (口) — giving the core sense of 'come together, join, fit.' From 'fit/match' it extended to 'combine, unite, agree' and to measure-word uses. The reading hé reflects this 'joining' meaning.