纽扣
niǔ koù · HSK 7
button
🔘 niǔ koù sounds like new coat, and a new coat is covered in buttons
纽 (niǔ) means knot or tie; 扣 (koù) means to fasten or clasp. Together a knot-fastener is a button. The sound niǔ-koù echoes new-coat, the thing whose buttons you do up.
扣 — hand radical 扌 + 口 (mouth/phonetic)
扣 is a phono-semantic compound: the hand radical 扌 signals an action done with the hand, while 口 (kǒu) supplies the sound. Its core sense is to knock, fasten, or buckle with the hand, later extending to deduct (as in deducting points) and to button up.