A double-breasted jacket, coat, or suit jacket has two sets of buttons on the front, and the cloth wraps across so that one side of the chest covers the other. You often see two rows of buttons; one row may do the real work of closing the coat, and the other may sit there for the look. The opposite is single-breasted: one row of buttons, the front meeting in a simple line. Double-breasted coats look a little more formal and square across the chest. They come in and out of fashion; in some decades they look smart, in others a bit old. Tailors and clothes shops still use the term as a plain description, not as slang. “Breasted” here is from the breast in the sense of the chest — the front of the garment — not from feeding a baby.