PLANARIAN Meaning of PLANARIAN in English [ plə'nɛ:rɪən ]■ noun Zoology a free-living aquatic flatworm. [Order Tricladida.]OriginC19: from mod. L. Planaria (genus name), feminine of L. planarius 'lying flat'. Concise Oxford English vocab. Сжатый оксфордский словарь английского языка. 2004