Green’s Dictionary of Slang

1. a Belgian.

[1608		E. Topsell Hist. of Serpents 96: Amongst the Belgies or Netherlanders, it is tearmed Spaensche Vlieghe].
1919		R.N. Johnson Heaven, Hell, or Hoboken 151: Guess the Frogs and Belgies thought we were pro-German.
1929		(con. 1917–18) C. MacArthur War Bugs 248: The Belgies now insisted that we sleep in their feather beds.
1976		Murder By Death [film script] I’m a Belgie, not a Frenchie.
1978		Maledicta II:1+2 (Summer/Winter) 151: Belgie Anyone from Belgium. Not commonly used in North America, but common in England and particularly in Agatha Christie mystery novels.

2. in attrib. use of sense 1.

1831

Dublin Morn. Register 22 Feb. 2/2: The Belgie deputation had their solemn audiences [...] when the King of the French delivered [...] his positive refusal of the crown of Belgium for the Duke of Nemours.