13 letters · 27 points in Scrabble
noun photosynthetic or plant constituent of plankton; mainly unicellular algae
originFrom phyto- + plankton. From Ancient Greek φυτόν (phutón, “plant”) + πλαγκτόν (planktón), neuter of πλαγκτός (planktós, “wandering”). However, they are no longer classified as plants, so the terminology is showing a historical meaning.
Etymology from Wiktionary, CC BY-SA 3.0