单调
dān diào · HSK 4
monotonous
单 (single) + 调 (tune) = one tune on repeat = monotonous
单 means single/sole and 调 means tune or tone. A single tune playing over and over is the definition of monotonous. Same 调 as in 音调 (pitch) and 调子 (melody).
单 — 叩 (two mouths 口) over 甲 (shield/armor)
Originally a pictograph of a forked hunting weapon or shield with two prongs at the top. The ancient form shows a Y-shaped tool, later stylized into the modern shape. The meaning shifted from the weapon to 'single' or 'one,' possibly because it was a single-handed tool.
调 — speech radical 讠(言) + 周 zhōu (phonetic)
调 is a semantic-phonetic compound. The 讠(言) radical signals 'speech' or 'words,' while 周 supplies the sound. Originally meaning to harmonize or coordinate through words, it later extended to 'tune,' 'adjust,' and 'melody' (read diào), and 'mix evenly' or 'mediate' (read tiáo).