痛快
tòng kuài · HSK 4
to one's heart's content
😄 痛快 = pain + fast — pain rushes out, leaving pure delight
痛 (pain/ache) + 快 (fast/quick). When pain leaves quickly, you feel relief and joy — hence delighted, to one's heart's content. Also used for doing things in a straightforward, no-holds-barred way.
痛 — sickness radical 疒 + 甬 (yǒng, phonetic)
痛 is a semantic-phonetic compound. The 疒 radical depicts a person on a sickbed and signals illness or pain. The component 甬 supplies the sound, historically close to 'tòng'. Together they convey bodily ache, later extended to emotional pain and the adverbial sense 'thoroughly'.
快 — heart radical 忄 + 夬 (phonetic)
快 is a semantic-phonetic compound. The heart radical 忄 carries the meaning, since the original sense referred to a feeling of pleasure or delight. The right side 夬 supplies the sound. The meaning later extended from 'pleased' to 'quick, fast', the dominant modern sense.