deep
沕 centers on the idea of depth, especially in a watery or obscure sense. The single given meaning 'deep' captures this core concept.
沕 combines 氵 (water) with 勿, which likely contributes a phonetic element. The exact historical development is uncertain, but the water radical suggests a connection to depth or obscurity in water.
Water 氵 beside 勿, a shape that looks like a deep, swirling pool. Picture the water sinking into a hidden, deep place.
For ブツ, imagine a deep pool where you drop a boot: the boot sinks deep into the water, and 'boot' cues ブツ.