The term PART OF AN ADIRONDACK CHAIR can be summarized by the crossword solution SLAT, which is a four-letter word. A SLAT is a thin, narrow strip of material, usually wood, that is used to form part of an Adirondack chair. Slats are typically arranged in a pattern and are connected together to form the back and seat of the chair. They provide support and comfort while also adding a decorative element to the chair.