～発
～はつ · ～hatsu · JLPT N2 · noun
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🔫 発 = fire off, set out: each hatsu is one shot that leaves the barrel
発 means to emit or depart, as in 出発 (departure) and 発射 (launch). The old form 發 contains 弓, the bow, so it began as letting an arrow fly. That's why it counts shots: 一発, 二発, and note the sound change in 三発 (sanpatsu).