From French (1796), from Proto-Indo-European '*pleth₂-' ("to spread, flat"), from PIE *pleth₂- ("to spread, flat").
An area of relatively level high ground; a state of little or no change following a period of activity or progress.
From French 'plateau' (a flat piece, a tray, a table-land), from Old French 'platel' (a flat piece of metal or wood), diminutive of 'plat' (flat, level), from Vulgar Latin '*plattus' (flat, broad), from Greek 'platús' (πλατύς, broad, flat, wide), from PIE root *pleth₂- (to spread, flat). The same root gives us 'plate,' 'platform,' 'platitude' (a flat remark), 'Plato' (the philosopher, whose name meant 'broad-shouldered'), and 'platypus' (flat-footed). The geographical sense of a high flat area emerged in the 18th century from French geographical writing about mountainous
The philosopher Plato's real name was Aristocles — 'Plato' was his wrestling nickname meaning 'broad' (from 'platús'), referring to his broad shoulders or broad forehead. His name shares a root with 'plateau,' 'platypus,' and 'platitude.' So a 'plateau' and a famous philosopher are both, etymologically, just 'the flat thing.'