沸騰
ふっとう · futtou · JLPT N1 · noun
boiling
♨️ 沸 (fèi) = boil, 騰 (téng) = rise up: the water boils and bubbles surge upward.
Read it as boil plus rise: 沸 is boiling water, 騰 is leaping upward, so 沸騰 is water surging up as it boils. The same word also means seething, as with a crowd or anger.