積もる
つもる · tsumoru · JLPT N3 · verb-godan
to pile up
❄️ 積 = stack (as in 積む); 積もる is what snow does: 雪が積もる
積む (tsumu) means you stack something yourself. 積もる (tsumoru) means it piles up by itself, like snow or dust. Sound hook: tsu-MORE-u, there's always more on the pile.