Etymology
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trap (n.)

"contrivance for catching unawares," late Old English træppe, treppe "snare, trap," from Proto-Germanic *trep- (source also of Middle Dutch trappe "trap, snare"), related to Germanic words for "stair, step, tread" (Middle Dutch, Middle Low German trappe, treppe, German Treppe "step, stair," English tread (v.)).

This is probably literally "that on or into which one steps," from PIE *dreb-, an extended form of a root *der- (1), base of words meaning "to run, walk, step." The English word is probably akin to Old French trape, Spanish trampa "trap, pit, snare," but the exact relationship is uncertain.

The sense of "deceitful practice, device or contrivance to betray one" is recorded from c. 1400. The meaning "U-shaped section of a drain pipe" is from 1833. Slang meaning "mouth" is from 1776. Speed trap is by 1908. Trap-door "door in a floor or ceiling" (often hidden and leading to a passageway or secret place) is attested from late 14c. (trappe-dore).

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trap (v.)
late 14c., "ensnare (an animal), catch in a trap; encircle; capture," from trap (n.) or from Old English betræppan. Figurative use is slightly earlier (late 14c.). Related: Trapped; trapping.
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death-trap (n.)

"structure or situation involving imminent risk of death," 1835, from death + trap (n.).

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rat-trap (n.)

"trap for catching rats," late 15c., rat trappe, from rat (n.) + trap (n.).

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sand-trap (n.)

1838, in hydraulics, "device for filtering impurities from water," from sand (n.) + trap (n.). As "golf bunker," by 1906.

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trapper (n.)
"one who traps animals" (for fur, etc.), 1768, agent noun from trap (v.).
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firetrap (n.)
also fire-trap, "place at great risk of destruction by fire and with insufficient means of escape," 1882, from fire (n.) + trap (n.).
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entrap (v.)
"to catch, as in a trap," 1530s, intrappe, from Old French entraper "trap, catch in a trap;" see en- (1) + trap (n.). Related: Entrapped; entrapping.
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traps (n.1)
"expanse of dark igneous rock," 1794, from Swedish trapp (Torbern Bergman, 1766), from trappa "stair," related to Middle Low German trappe "staircase" (see trap (n.)). So called from the step-like appearance of the rock.
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