偶数
ぐうすう · guusuu · JLPT N2 · noun
act
偶 = pair, 数 = number: even numbers split into two equal pairs
偶 appears in 配偶 (spouse) and 偶然 (by chance), both about two things matched up. Even numbers are the ones that pair off with nothing left over.
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'.