/ Dictionary / Index M mesoplankton: Meaning and Definition of Find definitions for: mes•o•plank•ton Pronunciation: (mez"u-plangk'tun, mes"-, mē"zu-, -su-), [key] — n. plankton that live at middle depths. planktonic organisms between 0.04 and 0.4 in. (1 mm and 1 cm) in length. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. mesophyte Mesopotamia Related Content Daily Word Quiz: panacea Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language