正解
せいかい · seikai · JLPT N1 · noun
right answer
正 — one 一 + stop 止
Originally an ideograph showing a foot (止) advancing toward a target line (一), meaning 'to march straight toward' a city or goal. From this came the senses 'upright,' 'correct,' and 'proper.' The military sense survives in 征 (to campaign), which took over the original 'march' meaning.
解 — horn 角 + knife 刀 + ox 牛
解 is an ideograph showing hands using a knife (刀) to separate the horn (角) from an ox (牛). The original meaning was to butcher or dismember an ox, which broadened to 'untie, separate, loosen,' and then extended figuratively to 'explain' or 'understand'—to take something apart mentally.