Etymology
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idle (adj.)

Old English idel "empty, void; vain; worthless, useless," from Proto-West Germanic *idla- (source also of Old Saxon idal, Old Frisian idel "empty, worthless," Old Dutch idil, Old High German ital, German eitel "vain, useless, mere, pure"), a word of unknown origin.

Subsequent developments are peculiar to English: sense "not employed, not doing work" was in late Old English in reference to persons; from 1520s of things; from 1805 of machinery. Meaning "lazy, slothful" is from c. 1300. In Elizabethan English it also could mean "foolish, delirious, wandering in the mind." Idle threats preserves original sense.

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idle (v.)
late 15c., "make vain or worthless" (trans.), from idle (adj.). Meaning "spend or waste (time)" is from 1650s. Meaning "cause to be idle" is from 1788. Intrans. sense of "run slowly and steadily without transmitting power" (as a motor) first recorded 1916. Related: Idled; idling. As a noun, 1630s of persons, 1939 of an engine setting.
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idler (n.)
"one who spends his time in inaction," 1530s, agent noun from idle (v.).
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idly (adv.)
Old English idellice "vainly;" see idle + -ly (2). From late 14c. as "in an idle or indolent way."
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idleness (n.)
Old English idelnes "frivolity, vanity, emptiness; vain existence;" see idle (adj.) + -ness. Old English expressed the idea we attach to in vain by in idelnisse. In late Old English it began to acquire its sense of "state of being unoccupied, doing no work, or indolent." Similar formation in Old Saxon idilnusse, Old Frisian idlenisse, Old High German italnissa. Spenser, Scott, and others use idlesse to mean "condition of being idle" in a positive sense, as a pleasure.
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fiddle (v.)
late 14c., "play upon a fiddle," from fiddle (n.); the figurative sense of "to act nervously, make idle movements, move the hands or something held in them in an idle, ineffective way" is from 1520s. Related: Fiddled; fiddling.
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babble (n.)
c. 1500, "idle talk," from babble (v.). In 16c., commonly in reduplicated form bibble-babble (1530s). Meaning "inarticulate speech" is from 1660s. Other nouns meaning "idle talk" included babblery (1530s), babblement (1640s).
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vaniloquence (n.)
"idle talk," 1620s, from Latin vaniloquentia, from vanus "idle, empty" (from suffixed form of PIE root *eue- "to leave, abandon, give out") + loquens, from loqui "to speak" (from PIE root *tolkw- "to speak").
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leisure (adj.)
"free from business, idle, unoccupied," 1660s, from leisure (n.).
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truant (adj.)
"idle, loitering, given to shirking duty or business," 1540s, from truant (n.).
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