pen, pencil

筆 is composed of the BuShou of 竹(bamboo) and 聿. 聿 depicts a hand holding a pen, means pen, pen is mostly made of bamboo in ancient China. On the other hand, 聿 has the same pronunciation as 遹 in the past, which is similar to the ancient pronunciation of 筆, both in present Cantonese still preserve such pronunciation.