沸く
わく · waku · JLPT N4 · verb-godan
to boil
♨️🫖 waku sounds like wok — a wok on the flame makes water boil
沸 = water radical 氵 + 弗 (phonetic), so the kanji itself says water doing something. 沸く is intransitive: the water boils on its own (お湯が沸く). Its transitive partner is 沸かす, to boil something.