歯磨き
はみがき · hamigaki · JLPT N2 · noun
toothbrushing
🪥🦷 歯 (tooth) + 磨き (polishing) = tooth-polishing, i.e. brushing teeth
The verb 磨く (migaku) means to polish or scrub, as with shoes or metal. Its noun form 磨き joins 歯 to name the whole act of cleaning teeth, toothpaste included as the cleaning agent.
磨 — stone 石 + hemp 麻 (phonetic)
A semantic-phonetic compound: 石 'stone' gives the meaning (grinding involves stones), while 麻 'hemp' supplies the sound. Originally referred to a millstone or the act of grinding grain, later extending to 'rub, polish, wear down' and figuratively 'to torment' or 'waste time'.