A lapel is literally a "little lap" — a small fold — and it evolved because soldiers folded back their coat fronts, turning a practical flap into a fashion statement.
The fold of cloth on each side of a coat or jacket immediately below the collar, which is folded back against the front of the garment.
A diminutive of lap (a fold, a flap), from Old English læppa (a skirt, the loose part of a garment, a lobe), from Proto-Germanic *lappō (a hanging piece, a flap). A lapel is literally a little lap — a small fold of fabric. Key roots: *lappō (Proto-Germanic: "hanging piece, flap, lobe").
The lapel evolved from a practical necessity: early coats had no fixed collar, and riders and soldiers turned up the front panels and buttoned them for protection against cold and wind. When unbuttoned and folded back, these panels became the lapel. The width and shape of lapels have been one of fashion's most reliable indicators