hydroponic UK /ˌhaɪdɹəˈpɒnɪk/US /ˌhaɪdɹəˈpɑnɪk/ adjective1 •Of a plant; pertaining to or grown using hydroponics, a method of growing plants using mineral nutrient solutions in water, without soil.Sid was now living in a small commune in the Shetland Islands, where he and his fellow communards were dedicated to the growing of implausibly large hydroponic onions. — 1991