噛み切る
かみきる · kamikiru · JLPT N1 · noun
to bite off
🦷 噛む (kamu, bite) + 切る (kiru, cut) = bite through until it comes off
Two verbs fused: 噛む bites and 切る cuts, so the teeth do the cutting. The 切る ending often signals finishing an action all the way through.
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.