The small or microscopic organisms that drift or swim weakly in a body of water, including bacteria, diatoms, jellyfish, and various larvae. Plankton is an important food source for fish and other larger organisms.
[German, from Greek, neuter of planktos, wandering, from plazein, to turn aside; see plāk-2 in the Appendix of Indo-European roots.]
plank·tonic (-tŏnĭk) adj.
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