The term 'CERTAIN CURTAIN' can be broken down into two crossword solutions: SWAG (4 letters) and SCRIM (5 letters). SWAG is a term used to describe a decorative fabric or drapery hung in a window or doorway, often with a pattern or fringe. SCRIM is a lightweight fabric used for theatrical backdrops, curtains, and other stage effects. Both fabrics are often used in the theater and film industry to create certain effects.