Date: 1800-1900 Language: German Origin: Greek, from planktos 'wandering', from plazesthai 'to wander' plankton noun Related topics: Biology, Animals, Plantsplank???ton [uncountable]HBPHBA the very small forms of plant and animal life that live in water, especially the sea, and are eaten by fish Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.