What does all that mumbo jumbo mean?
Fit and silhouette, while seemingly the same thing are two completely different ideas.
Fit describes the way a suit (or any garment for that matter) has been tailored, molded to the wearer's body. Simply put, Fit is the way a suit fits. A suit should ideally fit or wear like a second skin; if it doesn't then the suit has a poor Fit. One major thing that affects Fit are those pesky armholes, for if the armholes are not shaped and sized correctly to the specific customer then no amount of tailoring will help the rest of the suit fit right. A suit should fit the wearer in the shoulders, armholes, waist and hips.
Below is an example of a poorly fitted suit, courtesy of Thom Browne:
Silhouette describes the outward appearance of a suit. This, unlike Fit, can vary from suit to suit according to the wearer's preferences. We see great variance of Silhouette throughout the Golden Era: from the slim and trim of the 1920s, the natural and trim of the 1930s and the big and bulky of the 1940s and early 1950s to the slim and trim of the 1960s, full circle.
Silhouette is affected by the amount of padding in the shoulders, the amount of waist suppression (or lack thereof) and the length of the jacket just to name a few. And, while a suit can be made to fit nearly any body shape, certain silhouettes can only go with certain body shapes.
For example, a heavy man cannot have a well fitted suit with the same amount of waist suppression as a skinny tall man can. The physics of it just will not allow it to happen.
click to enlarge
So, which is more important? Fit or Silhouette? I would have to say Fit. A well fitted suit with poor silhouette is still well fitted and will be comfortable for the owner to wear, even if it makes him look like a blimp. A poorly fitted suit with great silhouette will be too uncomfortable for a man to wear and it will become a hated thing, a uniform. That is the problem with suits today: they are poorly fitted and so uncomfortable that most men hate them and wear them only when they must.
Suits shouldn't be uniforms. They should have both Fit and Silhouette.