切れる
きれる · kireru · JLPT N3 · verb-ichidan
to break
✂️🔪 切 = cut; kireru sounds like killer: a killer knife cuts well
The kanji 切 means cut, also in 切符 (kippu, ticket) and 大切 (taisetsu, important). 切れる is the intransitive form: the knife cuts well, a thread snaps, a phone line drops, stock runs out. A sharp person is also 切れる.
切 — 七 (phonetic) + 刀 (knife radical)
切 is a semantic-phonetic compound: 刀 'knife' gives the meaning of cutting, while 七 supplies the sound. The original sense was to slice or cut with a blade. From there it extended figuratively to 'close to' (as in pressed against) and 'urgent/earnest', as in 切实.