i·dle / ˈīdl/ • adj. (i·dler, i·dlest) 1. (esp. of a machine or factory) not active or in use: assembly lines standing idle for lack of spare parts. ∎  (of a person) not working; unemployed. ∎  (of a person) avoiding work; lazy. ∎  (of time) characterized by inaction or absence of significant activity: at no time in the day must there be an idle moment. ∎  (of money) held in cash or in accounts paying no interest.2. without purpose or effect; pointless: he did not want to waste valuable time in idle chatter. ∎  (esp. of a threat or boast) without foundation: I knew Ellen did not make idle threats.• v. [intr.] (of a person) spend time doing nothing; be idle: four men were idling outside the shop. ∎  [intr.] move aimlessly or lazily: Cal idled past MetroHealth at a stately pace. ∎  (of an engine) run slowly while disconnected from a load or out of gear: the car is noisily idling in the street. ∎  [tr.] cause (an engine) to idle. ∎  [tr.] take out of use or employment: he will close the newspaper, idling 2,200 workers.PHRASAL VERBS: idle something away spend one's time doing nothing or very little.DERIVATIVES: i·dle·ness n.

idle an idle brain is the devil's workshop those who do not apply themselves to their work are most likely to get into trouble (compare the Devil finds work for idle hands to do). The saying is recorded from the early 17th century.
idle people have the least leisure lazy people are the least able to manage their time efficiently (compare the busiest men have the most leisure). The saying is recorded from the late 17th century.

See also as good be an addled egg as an idle bird, the Devil finds work for idle hands to do at devil, it is idle to swallow the cow at swallow2.

idle †empty; worthless, useless; doing nothing, inactive OE.; lazy, indolent XIII. OE. īdel = OS. īdal empty, worthless (Du. ijdel), OHG. ītal (G. eitel), ult. orig. unkn. Primary meaning prob. ‘empty’.