A broad sash, especially one that is pleated lengthwise and worn as an article of formal dress, as around a man's waist together with a tuxedo or dinner jacket.
waistband
noun
A band of fabric encircling the waist, especially a part of a pair of pants or a skirt.
How often have the words cummerbund and waistband occurred in a corpus of books? (source: Google Ngram Viewer )