筷 is a comparatively late phono-semantic character. 竹, “bamboo”, supplies the meaning category, while 快 mainly supplies the sound. Earlier Chinese commonly used 箸 for chopsticks. A Ming-period account connects the newer word with boat people avoiding 箸 because it sounded like a word for stopping, but the exact path by which the replacement spread is not fully certain. This seal-form-inspired sketch keeps the bamboo top distinct above a compact 快.
A piece of culture
A pair at the family table 筷子 are used as a pair, with bamboo still familiar alongside wood, metal and reusable modern materials. At many Chinese tables, people avoid placing chopsticks upright in a bowl of rice because they can resemble incense offered for the dead. Customs vary, so a considerate guest follows the lead of the people sharing the meal.