pleu- / Indo-European roots
Examples of words with the root pleu-: flèche, fledge, flee, fleet, fletcher, fley, flight, flit, float, flood, flotilla, flotsam, flow, flue, flugelhorn, fluster, flutter, fly, fowl, fugleman, pleopod, pleuston, Pluto, plutocracy, pluvious, pneumo-, pneumonia, pneumonic, pulmonary, pyelitis.
▲ Derivatives include pulmonary, Pluto, flow, fowl, flutter, fluster.
I. Basic form *pleu-.
1. plover, pluvial, pluvious from Latin pluere, to rain.
2. pleopod from Greek plein (< *plewein), to swim.
3. pleuston from Greek pleusis, sailing.
4. Suffixed zero-grade form *plu-elos. pyelitis from Greek dissimilated puelos, trough, basin.
5. Suffixed form *pl(e)u-mon-, "floater" lung(s). a. pulmonary from Latin pulmō (< *plumonēs), lung(s); b. pneumo-, pneumonia, pneumonic from Greek pleumōn, pneumōn (influenced by pneuma, breath; see pneu-), lung.
6. Suffixed o-grade form *plou-to-. Pluto; plutocracy from Greek ploutos, wealth, riches (< "overflowing").
7. Lengthened o-grade form *plō(u)-. a. (i) flow from Old English flōwan, to flow; (ii) perhaps Middle Dutch vluwe, fishnet flue2 Both
(i) and (ii) from Germanic *flōwan, to flow; b. suffixed form *plō-tu-. flood from Old English flōd, flood, from Germanic *flōduz, flowing water, deluge.
II. Extended form *pleuk-.
1. fly1 from Old English flēogan, to fly, from Germanic *fleugan, to fly.
2. fly2 from Old English flēoge, a fly, from Germanic *fleugōn-, flying insect, fly.
3. Probably Germanic *fleuhan, to run away. flee from Old English flēon, to flee.
4. fley from Old English flȳgan, flēgan, to put to flight, from Germanic causative *flaugjan.
5. flèche, fletcher from Old French fleche, arrow, from Germanic suffixed form *fleug-ika.
6. Zero-grade form *pluk-. a. fledge from Old English *flycge, with feathers (only in unfligge, featherless), from Germanic *flugja-, feather; b. flight1, flight2 from Old English flyht, act of flying, and *flyht, act of fleeing, escape, from Germanic suffixed form *flug-ti-; c. fowl from Old English fugol, bird, from Germanic *fuglaz, bird, dissimilated from possible (but unlikely) suffixed form *flug-laz; d. flugelhorn, fugleman from Middle High German vlügel, wing, from Germanic suffixed form *flug-ilaz.
III. Extended form *pleud-.
1. fleet1, fleet2 from Old English flēotan, to float, swim (from Germanic *fleutan), and Old Norse fljōtr, fleet, swift (from Germanic *fleutaz).
2. Zero-grade form *plud-. a. (i) float from Old English flotian, to float; (ii) flotsam from Old French floter, to float. Both
(i) and (ii) from Germanic derivative *flotōn, to float; b. flotilla from Old Norse floti, raft, fleet; c. flutter from Old English floterian, flotorian, to float back and forth (-erian, iterative and frequentative suffix); d. flit from Old Norse flytja, to further, convey, from Germanic *flutjan, to float. a-d all from Germanic *flut-, *flot-.
3. fluster probably from a Scandinavian source akin to Icelandic flaustr, hurry, and flaustra, to bustle, from Germanic *flausta-, contracted from suffixed form *flaut-stā-, probably from *pleud-, o-grade *ploud-.
[Pokorny pleu- 835, pl(e)u-mon- 837.]