1A bomb; an explosive device designed to detonate and cause destruction. Also used figuratively (e.g. 爆弾発言, 'bombshell remark').
空港の手荷物検査で爆弾のようなものが見つかり、大騒ぎになった。
Something resembling a bomb was found at the airport baggage check, causing a big commotion.
この辺りは戦争中、爆弾が何度も落とされた場所だ。
This area was bombed many times during the war.
あの政治家の記者会見での発言はまさに爆弾発言だった。
That politician's remarks at the press conference were truly a bombshell.
2A slang bar term for a strong mixed drink made by adding one alcohol to another (e.g. whisky poured into beer, or an extra-strong shōchū highball); usually written in kana.
「ばくだんを一杯ください」と常連客が注文した。
"One 'bakudan,' please," the regular customer ordered.
あの店のばくだんはウイスキーが多めで、かなり強い。
That bar's 'bakudan' has a lot of whisky in it and is quite strong.