also *pletə-, Proto-Indo-European root meaning "to spread;" extension of root *pele- (2) "flat; to spread."
It forms all or part of: clan; flan; flat (adj.) "without curvature or projection;" flat (n.) "a story of a house;" flatter (v.); flounder (n.) "flatfish;" implant; piazza; place; plaice; plane; (n.4) type of tree; plant; plantain (n.2); plantar; plantation; plantigrade; plat; plate; plateau; platen; platform; platinum; platitude; Platonic; Plattdeutsch; platter; platypus; plaza; supplant; transplant.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit prathati "spreads out;" Hittite palhi "broad;" Greek platys "broad, flat;" Latin planta "sole of the foot;" Lithuanian platus "broad;" German Fladen "flat cake;" Old Norse flatr "flat;" Old English flet "floor, dwelling;" Old Irish lethan "broad."
"habitual loafer, idle man about town," 1854, from French flâneur, from flâner "to stroll, loaf, saunter," probably from a Scandinavian source (compare Old Norse flana "to wander aimlessly," Norwegian flana, flanta "to gad about"), perhaps from PIE root *pele- (2) "flat; to spread." Related: flânerie.
The Welsh origin is not a universally accepted etymology, due to the sound changes involved; Barnhart, Gamillscheg, Diez suggest the English word is from an Anglo-French diminutive of Old French flaine "a kind of coarse wool." Modern French flanelle is a 17c. borrowing from English.
"slender, pointed missile weapon, made to be shot from a bow," early 14c., from Old English arwan, earlier earh "arrow," possibly borrowed from Old Norse ör (genitive örvar), from Proto-Germanic *arkhwo (source also of Gothic arhwanza), from PIE root *arku-, source of Latin arcus (see arc (n.)). The etymological sense would be "the thing belonging to the bow." The meaning "a mark like an arrow" in cartography, etc. is from 1834.
It was a rare word in Old English. More common words for "arrow" were stræl (which is cognate with the word still common in Slavic and once prevalent in Germanic, related to words meaning "flash, streak") and fla, flan (the -n perhaps mistaken for a plural inflection), from Old Norse, a North Germanic word, perhaps originally with the sense of "splinter." Stræl disappeared by 1200; fla became flo in early Middle English and lingered in Scottish until after 1500.
Robyn bent his joly bowe,
Therein he set a flo.
["Robyn and Gandelyn," in a minstrel book from c. 1450 in the British Museum]