A Greatcoat is generally a big, bulky overcoat such as an Ulster or a British Warm. Often, greatcoats have a military background. An overcoat is a heavy coat that is worn on top of a suit or a jacket. As such, all greatcoats are overcoats but not all overcoats are greatcoats.
A duffel coat, or duffle coat (standard UK spelling), is a coat made from duffel, a coarse, thick, woollen material. The name derives from Duffel, a town in the province of Antwerp in Belgium where the material originated. Duffel bags were originally made from the same material.
A bridge coat is a pea coat that extends to the thighs, and is a uniform exclusively for officers and chief petty officers. The reefer is for officers and chief petty officers only, and is identical to the basic design but usually has gold buttons and epaulettes. Only officers wear the epaulettes.
: The mac, short for macintosh, not the computer, came from Scotland, and the trench from England. The mac is older (born in 1823). The trench was born in the trenches during World War I. Both are perennial raincoat favorites for men (and many women) and have graduated into many other-than-water-repellent fabrics.
Trench coat. A trench coat or trenchcoat is a raincoat made of waterproof heavy-duty cotton gabardine drill, leather, or poplin. It generally has a removable insulated lining, raglan sleeves, and the classic versions come in various lengths ranging from just above the ankles (the longest) to above the knee (the shortest).