The term 'chair-back part' refers to the components of a chair that form the back. The two crossword solutions for this term are SPLAT (5 letters) and SLAT (4 letters). SPLAT is an acronym for Spindle, Post, Leg, Arm, and Top rail, which are the five components that make up the back of a chair. SLAT is a thin strip of wood or metal that is used to support the back of a chair. Both SPLAT and SLAT are essential parts of a chair's back, providing support and structure.