In the Democratic Republic of the Congo (formerly Zaire): a man's suit consisting of a short-sleeved collarless jacket and loose trousers.
The wearing of shirts and ties was outlawed by President Mobutu for the majority of his time in power (1965–97), as symbolic of the country's colonial past, and the abacost promoted as the national costume and worn by his supporters. The abacost was also adopted as official costume in the 1970s by some other African countries.
1970s; earliest use found in The New York Times. From African French (Congo) abacost, abacos, apparently shortened from the French slogan à bas le costume, literally ‘down with the (Western) suit’ from à bas down, downwards + le, masculine definite article + costume suit.