Noun
An overcoat.
Source: Webster's dictionaryHell and damnation, life is such fun with a ragged greatcoat and a Jerry gun! Alexander Blok
Epaulettes were a detachable dress item worn only with tunic or greatcoat for parade or off duty wear. Source: Internet
Thus a legionnaire might parade or walk out in blue tunic and white trousers in hot weather, blue tunic and red trousers in normal temperatures or wear the blue greatcoat with red trousers under colder conditions. Source: Internet