ボツ, モツ, おぼ.れる, しず.む, ない
drown, sink, hide, fall into, disappear, die
JLPT1 G7 S7 F1385
The relevant seal inscription form shows that the right-hand element# (traditionally written as per the right-hand element of 歿) was originally swirling water + a hand → body dimly visible in the water in which it is submerged (compare 沈). 水 water was appended for emphasis/clarification → *sink* → *die*.
[Full Kanji Etymology List]