trapfall (n.)

c. 1200, "a falling to the ground; a dropping from a height, a descent from a higher to a lower position (as by gravity); a collapsing of a building," from Proto-Germanic *falliz, from the source of fall (v.). Old English noun fealle meant "snare, trap."

Of the coming of night from 1650s. Meaning "downward direction of a surface" is from 1560s, of a value from 1550s. Theological sense, "a succumbing to sin or temptation" (especially of Adam and Eve) is from early 13c.

The sense of "autumn" (now only in U.S. but formerly common in England) is by 1660s, short for fall of the leaf (1540s). Meaning "cascade, waterfall" is from 1570s (often plural, falls, when the descent is in stages; fall of water is attested from mid-15c.). The wrestling sense is from 1550s. Of a city under siege, etc., 1580s. Fall guy is attested by 1906.

"contrivance for catching unawares," Middle English trappe, from late Old English træppe, treppe "snare, trap" (for taking game or other animals), 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 (Watkins) 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 also is probably akin to Old French trape, Spanish trampa "trap, pit, snare," but the exact relationship is uncertain.

Figurative use is by c. 1200 in theology. The sense of "deceitful practice, device or contrivance to betray one unawares" is recorded from c. 1400.

The meaning "U-shaped section of a drain pipe," to prevent passage of air or gases through the pipe, is from 1833. The slang meaning "mouth" is attested by 1776.

It is attested from 1590s as the name of the pivoted wooden instrument used to throw in the game of trap-ball (short for trap-stick; trap-sticks as a figure of thin legs is by 1714). By 1812 it was extended to any device for sudden throwing or releasing by means of a spring, etc. Hence trap-shooting (by 1892).

In some specialized senses it has converged with provincial trap words for "stairs" from Low German and Scandinavian (see trap (n.2)). Also compare rattletrap.