From Middle Dutch 'dapper' (brave, bold) — shifted from martial courage to fashionable neatness, while Dutch kept the original brave meaning.
Neat and trim in dress and appearance; typically used for men.
From Middle Dutch 'dapper' meaning 'brave, bold, strong.' The original meaning was martial — a dapper warrior was a fierce one. The meaning shifted from 'bold in battle' to 'bold in appearance' to 'neatly dressed.' Key roots: dapper (Middle Dutch: "brave, bold").
In Dutch, 'dapper' still means 'brave' — it never made the shift to fashion that the English word did. German 'tapfer' (brave, courageous) is the same word. Calling someone 'dapper' in English is a fashion compliment; saying 'dapper' in Dutch is calling them a warrior. The word went from battlefield courage to coordinating pocket squares, which is either a cultural evolution or a significant downgrade, depending on your values.