From the 28 January, 1957 Life Magazine- Stylish Slouch: Spring suits-and wearers-take on a relaxed look.

'In shopping for a new suit this season, the word to remember is 'relax'. Grown nostalgic for the 1930's, U.S. designers are showing slouch suits influenced by the great Parisian designer Chanel.  Casual and easy fitting- to make the wearer look younger, says Chanel- these suits have pockets to lean on and hipbone-length jackets worn open wide. Blouses, an integral part of the suit, are often specially designed for them.  Made of soft tweed or jersey, the suits are worn with felt hats  which fit the head, or more casual still, with no hat. Women who are used to trim suits may consider the slouch models untidy- and there is real danger that wearers who carry the fashion too far will wind up looking sloppy rather than casual.

Casual outfits for spring are pale tweed suit with a short jacket and dotted blouse (Ben Zuckerman, $245) and a similar suit of wool and silk tweed with a silk blouse (Ben Zuckerman, $235).'

Again we can see that the definition of casual in 1957 is very different from what is considered casual today. The above two suits would be seen as quite formal in our current age.