1. one shot; one charge; one explosion
こっちの弾は一発しかない。I've only got one bullet.
2. one blow; one punch
一発殴るのが精一杯でさ。One punch was all I could manage, you know.
3. home run
4. one try; one attempt
そのとき一発で決めたら、カッコいいでしょう？If you nail it in one shot at that moment, it would be cool, wouldn't it?
5. win on the first go-around after calling rīchi
6. ippatsu (comp. karuta); taking a card which is read immediately after sending it