刻苦
kè kǔ · HSK 7
hardworking
⛏️ 刻 carve + 苦 bitter = carve away at bitter toil, i.e. grind hard
刻 — knife radical 刂 + 亥 (phonetic)
A semantic-phonetic compound. The right side 亥 supplies the sound, while the knife radical 刂 on the right gives the meaning, since 刻 originally referred to carving or engraving with a blade. From 'to carve' it extended to marking time notches on a sundial, hence the modern sense of 'a moment' or 'quarter hour'.
苦 — grass radical 艹 + 古 (old)
Originally referred to a bitter-tasting plant, with the grass radical 艹 indicating its botanical nature and 古 providing the phonetic element. The meaning extended from the literal bitter taste to figurative senses of hardship, suffering, and painful effort.