钢笔
gāng bǐ · HSK 5
fountain pen
🖋️ 钢 (steel) + 笔 (pen/brush) = steel pen = fountain pen
钢 means steel or hard metal; 笔 is the general word for writing instrument (brush, pen). A steel-tipped pen is a fountain pen, contrasted with 铅笔 (lead pen = pencil) and 毛笔 (hair pen = brush).
钢 — metal radical 钅 + 冈 (gāng, ridge)
A semantic-phonetic compound: the metal radical 钅 (simplified from 金) signals the meaning 'metal,' while 冈 supplies the sound 'gāng.' Originally referring to refined, hardened iron, 钢 came to mean 'steel,' and by extension the qualities of strength and rigidity.
笔 — bamboo radical 竹 (⺮) + 毛 (hair/fur)
Originally written 筆, depicting a writing brush: 竹 (bamboo) on top for the shaft and 毛 (hair) below for the bristles. Early brushes were bamboo handles tipped with animal hair. The simplified form 笔 keeps the same logic, just replacing the lower component directly with 毛.