sack coat

a short coat or jacket with a straight back and no seam at the waist.

Origin of sack coat

First recorded in 1840–50

sack-coat·ed, adjective

Putting his hand into the side-pocket of his sack-coat, he drew from it a small revolver.

Down South |Oliver Optic
Had the opportunity come to him, he would have worn a silk hat with a sack-coat, or a dress suit in the afternoon.

Last of the Great Scouts |Helen Cody Wetmore
On this occasion he wore a sack-coat of medium length, with side-pockets.

The Journal of Negro History, Volume 7, 1922 |Various
With it the sack-coat, or pilot-jacket, burrowed its way in, the cut and insignia of these showing many variations.

From Sail to Steam, Recollections of Naval Life |Captain A. T. Mahan

Heathcote, with his hands in the pockets of his sack-coat, walked up and down, listening.

Anne |Constance Fenimore Woolson