idler

First recorded in 1525–35; idle + -er¹

before 900; 1915–20 for def 12; Middle English, Old English īdel (adj.) empty, trifling, vain, useless; cognate with German eitel

1. Idle, indolent, lazy, slothful apply to a person who is not active. To be idle is to be inactive or not working at a job. The word is sometimes derogatory, but not always, since one may be relaxing temporarily or may be idle through necessity: pleasantly idle on a vacation; to be idle because one is unemployed or because supplies are lacking. The indolent person is naturally disposed to avoid exertion: indolent and slow in movement; an indolent and contented fisherman. The lazy person is averse to exertion or work, and especially to continued application; the word is usually derogatory: too lazy to earn a living; incurably lazy. Slothful denotes a reprehensible unwillingness to carry one's share of the burden: so slothful as to be a burden on others. 11. See loiter.

The English adjective idle comes from Old English īdel, originally meaning “empty” and also “useless, worthless.” The sense (used of people) “unemployed, out of work” dates from the 10th century. The rather harsher meaning “avoiding work, lazy, indolent” dates from the 14th century.
One of the senses of the verb idle, “to spend one’s time doing nothing,” dates from the 17th century and is first recorded in Samuel Pepys’ Diary.
The mechanical sense, used of a motor or engine disengaged from its load and operating at a low speed, dates from the 20th century.