Larousse housse - [de vêtements] suit sack

sack' dress" - a loose, unbelted dress that hangs straight from the shoulder to the hemline.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.
http://www.infoplease.com/dictionary/sack dress

sack dress - • noun a woman’s loose unwaisted dress, originally fashionable in the 1950s.
http://www.askoxford.com/concise_oed/sackdress?view=uk


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Note added at 12 hrs (2008-01-23 16:22:58 GMT)
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Black wool sack dress
Designed by Balenciaga, Paris, 1959-60
Balenciaga began to experiment with the sack dress during the fifties. The simple, loose style was the opposite of the more common nipped-in waist of that era and looked forward to the 1960s shift dress.
http://www.vam.ac.uk/vastatic/microsites/1211_sixties/balenc...

Balenciaga
In 1951, he totally transformed the silhouette, broadening the shoulders and removing the waist. In 1955, he designed the tunic dress, which later developed into the chemise dress[3] of 1958. Other contributions in the postwar era included the spherical balloon jacket (1953), the high-waisted baby doll dress (1957), the cocoon coat (1957), the balloon skirt (1957), and the **sack dress** (1957).
http://en.wikipedia.org/wiki/Balenciaga

You may have heard someone, most likely and extremely fashion forward person, mention wearing a "sack" or a "sack dress". It may confuse those who are just hearing about this trend for the first time, but it won't be for long. Sack dresses, shift dresses and shirt dresses are hitting the fashion scene in a big way. The one thing all these dresses have in common is that they're loose, rather shapeless and lack a defined waist. However their silhouettes differ.

The shift dress of today hangs straight to the ground, usually with a slight a line. Shirt dresses are basically a longer version of a button front, woven shirt, and are usually the most fitted of the three. **The sack dress is much looser and often rounded throughout the bodice and skirt.** And to tell the truth, this trend isn't entirely new. Top designers such as Balenciaga and Chloe sent these looks down the runway early last year, as a part of their Spring/Summer 2006 collection, and celebrities such as Nicki Hilton were seen wearing these dresses earlier this year. Slowly, these garments are making their way into the mainstream, but it takes a bit of hunting to find them online.

… **They have a Catharine Malandrino pointelle sweater sack dress, which embodies what a sack dress should perfectly with it's rounded hips. It comes in ivory and gray, and rings up at a steep $325. For those not quite as daring in their fashion choices, Daryl K makes a great black dress which is a cross between a sack and a tunic. It is belted at the waist, which makes it more flattering on a broader range of figures, but it's gathered at the bottom to emphasize the look of a sack.**
http://www.associatedcontent.com/article/84696/where_to_buy_...

robe tube – shift dress
Robe droite dont la taille, non coupée, et l’ourlet ont le meme diamètre
Vocabulaire de l’habillement de Céline Dupré et de Françoise Hudon

shift - 5 a straight unwaisted dress. 6 historical a long, loose undergarment
http://www.askoxford.com/concise_oed/shift?view=uk

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Note added at 16 hrs (2008-01-23 21:01:51 GMT) Post-grading
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Thanks, Yolanda! :-)