A tap-root is a long, thick, central root that grows underground on a plant. It helps the plant absorb nutrients and water from deep within the soil. Synonyms for tap-root include pivot root, main root, central root, and rooting depth. A pivot root is a single root that grows straight down from the stem or seed of a plant, while a central root is the main root that grows deep and wide from the center of the plant's base. Rooting depth refers to the overall depth of all the plant's roots combined. Understanding synonyms for tap-root and their meanings is helpful in gardening, farming, and landscaping.