The term 'CERTAIN SOFA' can be broken down into two crossword solutions: SLEEPER (7 letters) and SETTEE (6 letters). A SLEEPER sofa, also known as a sofa bed, is a type of sofa that can be converted into a bed. It typically has a metal frame and a mattress that folds out from the back or side of the sofa. A SETTEE is a type of sofa with a back and arms, usually upholstered, and often designed to seat two or three people.