drown
歾 centers on death by drowning. The given meaning is a single, narrow sense, so the core idea is simply to drown.
歾 is a rare character combining 歹 (death) with 勿, which likely contributes a phonetic element. The exact historical development is uncertain.
The left side 歹 suggests death, and the right side 勿 looks like a person flailing in water. Picture a drowning person's final struggle.
For ボツ, imagine a drowning person sinking like a heavy boat: boat -> ボツ, and the boat disappears under the water.