Definition of "skivvies"

My skivvies disappeared in surgery, a sinister conjunction of circumstance.

1993, William S. Burroughs, edited by Oliver Harris, The Letters of William S. Burroughs, 1945–1959, New York: Penguin, page 149

Then she pulled his pants down around his knees. He had a pair of old gray-and-white tight skivvies on. They were worn and threadbare and tight around his groin.

2001, Joe Meno, How the Hula Girl Sings, published 2005, page 165

“I brought some jeans, a sweater, a heavy shirt, some thermal socks and some skivvies.” He replied.“Skivvies?” A questioning look wrinkled her forehead.“Undershirts and underpants.” He explained.

2002, Chuck Frazier, Decades, iUniverse, page 89

Everyone in 2nd platoon had two pairs of boots, two pairs of utilities and several pair of skivvies, which served no purpose in Nam. No one wore skivvies because of the intense heat and it took only one case of heat rash, affectionately named “crotch rot,” to impress on us that skivvies were better suited as rags to clean weapons and tools.

2002, James R. Kelly, Casting Alpha: Amtracs in Vietnam, page 86

And the ceiling is so low that the man dancing on the bar, in nothing but his skivvies, was hunched over like a gorilla.

2005 March 13, Denny Lee, “Looking for Mr. Right Now”, in New York Times‎