税関
ぜいかん · zeikan · JLPT N2 · noun
customs
🛃 税 (tax) + 関 (barrier, gate) = the border gate where tax on goods is collected
関 means barrier or checkpoint, as in the historic 関所 (sekisho). Tax plus checkpoint gives customs, the border post where duties are collected.
税 — grain radical 禾 + 兑 (exchange/phonetic)
税 combines 禾 (grain) with 兑 (exchange), which also hints at the sound. In ancient China taxes were paid in grain, so the character originally meant a levy of harvest given to the state. Its meaning later broadened to taxes and duties of any kind.