fleetyoudaoicibaDictYouDict[fleet 词源字典]
fleet: [OE] Fleet is one of a vast tangled web of words which traces its history back ultimately to Indo-European *pleu-, denoting ‘flow, float’ (amongst its other English descendants are fly, flood, flow, fledge, fowl, plover, and pluvial). Fleet itself comes from the extended Indo- European base *pleud-, via the Germanic verb *fleutan and Old English flēotan ‘float, swim’ (modern English float comes from the related Old English flotian).

The verb has now virtually died out, but it survives in the form of the present participial adjective fleeting, which developed the sense ‘transient’ in the 16th century, and in the derived noun fleet: Old English seems to have had two distinct nouns flēot based on the verb flēotan, one of which meant ‘ships’, and the other of which signified ‘creek, inlet’ (it survives in the name of London’s Fleet Street, which runs down to the now covered-up Thames tributary, the river Fleet).

The adjective fleet ‘quick’ (as in ‘fleet of foot’) was probably borrowed from Old Norse fljótr, likewise a descendant of Germanic *fleut-.
=> fledge, float, flood, flow, fowl, plover, pluvial[fleet etymology, fleet origin, 英语词源]
fleet (n.)youdaoicibaDictYouDict
Old English fleot "a ship, raft, floating vessel," also, collectively, "means of sea travel; boats generally," from fleotan "to float" (see fleet (v.)). Sense of "naval force, group of ships under one command" is in late Old English. The more usual Old English word was flota "a ship," also "a fleet; a sailor." The fleet for "the navy" is from 1712.

The Old English word also meant "estuary, inlet, flow of water," especially the one into the Thames near Ludgate Hill, which lent its name to Fleet Street (home of newspaper and magazine houses, standing for "the English press" since 1882), Fleet prison (long used for debtors), etc.
fleet (adj.)youdaoicibaDictYouDict
"swift," 1520s, but probably older than the record; apparently from or cognate with Old Norse fliotr "swift," from Proto-Germanic *fleuta, which is related to the source of fleet (v.). Related: Fleetness.
fleet (v.)youdaoicibaDictYouDict
Old English fleotan "to float; drift; flow, run (as water); swim; sail (of a ship)," from Proto-Germanic *fleutan (cognates: Old Frisian fliata, Old Saxon fliotan "to flow," Old High German fliozzan "to float, flow," German fliessen "to flow, run, trickle" (as water), Old Norse fliota "to float, flow"), from PIE root *pleu- "to flow, swim" (see pluvial).

Meaning "to glide away like a stream, vanish imperceptibly" is from c. 1200; hence "to fade, to vanish" (1570s). Related: Fleeted; fleeting.