木板
mùbǎn · HSK 7
slab
🪵 木板 = 木 wood + 板 board, so a wooden plank
木 means wood or tree; 板 means board or plank on its own. Stuck together they name the concrete thing: a flat board of wood, a plank or batten.
板 — wood radical 木 + 反 (fǎn, phonetic)
板 is a semantic-phonetic compound. The 木 'wood' radical signals the meaning — a flat piece of wood, i.e. a board or plank. The right side 反 supplies the sound, historically close to 'bǎn/pàn'. Over time it extended to mean any flat panel, and figuratively 'stiff' or 'inflexible'.