Etam Black Satin Maxi Slip Dress or Gown with Side Slit size L

Etam gown in good condition, not much wear but there may be a few very tiny snags. The satin is rich and has a soft, matte underside. I’m not sure if item is a dress, or nightgown, but I suppose it could be either one. The back is adjustable with tie and there are darts at the bust line. There's a side slit on the left. The fabric has some give but not exceedingly stretchy. App'x 18 inches pit to pit and 17 at waist, about 52 long.