(military, slang, historical) Long, dark-coloured underwear worn by the WAAF in winter.
Coordinate term:twilights
1995, Beryl E. Escott, Our Wartime Days: The WAAF in World War 2, page 35:
[…] her blackouts. When the Officer inspected everything went well. The only thing was that two of our WAAF were not wearing any knickers at all!
2011 December 13, Peter Liddle, Captured Memories, 1930–1945: Across the Threshold of War: The Thirties and the War, Casemate Publishers, →ISBN, →OCLC: