倒数
dào shǔ , dào shù · HSK 7
to count backwards
⏳🔟 倒 = inverted/reverse + 数 = count → counting in reverse
倒 means upside-down or backwards. 数 means to count or a number. Together they literally say reverse-count — a countdown. As a noun (dào shù), it means countdown; as a verb (dào shǔ), it means to count backwards from a number down to zero.
倒 — person radical 亻 + 到 (to arrive)
倒 is a semantic-phonetic compound: the person radical 亻 gives meaning (an action done by/to a person), while 到 supplies the sound 'dào'. Originally meaning 'to fall over' (a person toppling), it extended to 'invert, upside down, pour out', as when something falls and spills.
数 — 婁 (lóu, phonetic) + 攵 (action radical)
数 is a phono-semantic compound. The right side 攵 (a hand holding a stick) suggests an action, originally tallying or counting by striking marks. The left side 婁 supplies the sound. Over time the meaning broadened from 'to count' to 'number' and 'several'.