idle: [OE] ‘Lazy’ is only a secondary meaning of idle. It originally meant ‘useless, worthless’ (as in ‘idle threats’), and the sense ‘lazy’ did not develop until the 13th century (the Old English words for ‘lazy’ were slow and slack). Idle is shared by other West Germanic languages, and its relatives (German eitel ‘vain, futile’ and Dutch ijdel ‘vain, useless, conceited’) point up its original English meaning, but it is not known what its ultimate origins are. [idle etymology, idle origin, 英语词源]