正門
せいもん · seimon · JLPT N2 · noun
gate
🚪 正門 = 正 (main, proper) + 門 (gate), so the main gate or main entrance
正 means main or correct, as in 正面 (front face). 門 means gate, as in 校門 (school gate). Together they name the principal entrance of a building or campus.
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.