The word "笔记" is formed through semantic compounding, where two independent characters, each with their own meaning, are combined to create a new, unified concept. The first character, "笔" (bǐ), means "pen" or "writing brush", representing the tool. The second character, "记" (jì), means "to record" or "to note down", representing the action. When merged, the literal sense of "pen-record" evolves conceptually to mean "notes" or "written records", effectively capturing the idea of material recorded with a writing instrument.