砕
サイ, くだ.く, くだ.ける
smash, break, crush, familiar, popular
JLPT1 G7 S9 F1579
As per
卒
# (compact) +
石
stone → *break down/crush/pulverize* stones (compare
破
and
拓
) → *smash* → *rack one's brains*; *wane*.
[Full Kanji Etymology List]