Etymology
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burden (n.1)

"a load, that which is borne or carried," Old English byrðen "a load, weight, charge, duty;" also "a child;" from Proto-Germanic *burthinjo- "that which is borne" (source also of Old Norse byrðr, Old Saxon burthinnia, German bürde, Gothic baurþei), from PIE root *bher- (1) "to carry," also "to bear children."

The shift from -th- to -d- began early 12c. (compare murder (n.), rudder, afford). Archaic burthen is occasionally retained for the specific sense of "capacity of a ship." Beast of burden is from 1740. Burden of proof (Latin onus probandi) "obligation on one party in an action to establish an alleged fact by proof" is recorded from 1590s.

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burden (n.2)
"leading idea, main topic," 1640s, a figurative use (on the notion of "subject often repeated") of the earlier sense "refrain or chorus of a song," 1590s, originally "bass accompaniment to music" (late 14c.), from Old French bordon (Modern French bourdon) "bumble-bee, drone," or directly from Medieval Latin burdonom "drone, drone bass" (source also of Spanish bordon, Portuguese bordão, Italian bordone), of echoic origin.
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burdensome (adj.)
"heavy, wearisome," 1570s, from burden (n.1) + -some (1). Earlier was burdenous (1520s). Related: Burdensomeness.
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overburden (v.)

also over-burden, "to put too much weight on, load with too great a burden," 1530s, from over- + burden (v.). Earliest uses are figurative. Related: Overburdened; overburdening.

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unburden (v.)
1530s, "to unload" (transitive), from un- (2) "reverse of" + burden (v.). Similar formation in German entbürden. Reflexive sense is recorded from 1580s. Related: Unburdened; unburdening.
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thither (adv.)
Old English þider "to or toward that place," altered (by influence of its opposite hider) from earlier þæder "to that place," from Proto-Germanic *thadra- (source also of Old Norse þaðra "there," Gothic þaþro "thence"), from PIE pronominal root *to- (see that) + PIE suffix denoting motion toward (compare Gothic -dre, Sanskrit -tra). The medial -th- developed early 14c. but was rare before early 16c. (compare gather, murder, burden).
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rudder (n.)

mid-15c. (late 12c. as a surname), a variation or alteration of Middle English rother, from Old English roðor "paddle, oar," from Proto-Germanic *rothru- (source also of Old Frisian roðer, Middle Low German roder, Middle Dutch roeder, Dutch roer, Old High German ruodar, German Ruder "oar"), from *ro- "steer" (from PIE root *ere- "to row") + suffix *-þra, used to form neutral names of tools.

The original sense is obsolete. The meaning "broad, flat piece of wood attached to the stern of a boat and guided by a tiller for use in steering" is from c. 1300. For shift of -th- to -d- compare burden (n.1), murder (n.); simultaneous but opposite movement turned -d- to -th- in father (n.), etc.

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spider (n.)

late 14c., spydyr, spither, from earlier spiþre, spiþur, spiþer (mid-14c.), from Old English spiðra, from Proto-Germanic *spin-thron- (cognate with Danish spinder), literally "spinner," from PIE root *(s)pen- "to draw, stretch, spin" + formative or agential *-thro. The connection with the root is more transparent in other Germanic cognates (such as Middle Low German, Middle Dutch, Middle High German, German spinne, Dutch spin "spider").

The male is commonly much smaller than the female, and in impregnating the female runs great risk of being devoured. The difference in sizes is as if the human female should be some 60 or 70 feet tall. [Century Dictionary]

The loss of -n- before spirants is regular in Old English (compare goose (n.), tooth). For shift of -th- to -d- compare murder (n.), burden (n.), rudder.

Not the common word in Old or Middle English, which identified the creatures as loppe (Chaucer's usual word), lobbe. Old English also had atorcoppe (Middle English attercop, literally "poison-head"), and (from Latin aranea), renge; Middle English had araine, "spider," via Old French from the same Latin word; see arachnid). Another Old English word was gangewifre "a weaver as he goes."

In literature, often a figure of cunning, skill, and industry as well as venomous predation; in 17c. English used figuratively for venomousness and thread-spinning but also sensitivity (to vibrations), lurking, independence. As the name for a type of two-pack solitaire, it is attested from 1890, probably based on resemblance of the layout of the decks in the original form of the game (see "Tarbart," "Games of Patience," 1901, p. 49). Spider crab is from 1710, used of various species; spider monkey is from 1764, so called for its long limbs.

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