Etymology
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wed (v.)

Old English weddian "to pledge oneself, covenant to do something, vow; betroth, marry," also "unite (two other people) in a marriage, conduct the marriage ceremony," from Proto-Germanic *wadja (source also of Old Norse veðja, Danish vedde "to bet, wager," Old Frisian weddia "to promise," Gothic ga-wadjon "to betroth"), from PIE root *wadh- (1) "to pledge, to redeem a pledge" (source also of Latin vas, genitive vadis "bail, security," Lithuanian vaduoti "to redeem a pledge"), which is of uncertain origin.

The sense has remained closer to "pledge" in other Germanic languages (such as German Wette "a bet, wager"); development to "marry" is unique to English. "Originally 'make a woman one's wife by giving a pledge or earnest money', then used of either party" [Buck]. Passively, of two people, "to be joined as husband and wife," from c. 1200. Related: Wedded; wedding.

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unwed (adj.)
1510s, from un- (1) "not" + past participle of wed (v.). Unwedded "unmarried; celibate" is from c. 1200.
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*wed- (1)
Proto-Indo-European root meaning "water; wet."

It forms all or part of: abound; anhydrous; carbohydrate; clepsydra; dropsy; hydra; hydrangea; hydrant; hydrargyrum; hydrate; hydraulic; hydro-; hydrogen; hydrophobia; hydrous; Hydrus; inundate; inundation; kirsch-wasser; nutria; otter; redound; redundant; surround; undine; undulant; undulate; undulation; vodka; wash; water (n.1); wet; whiskey; winter.

It is the hypothetical source of/evidence for its existence is provided by: Hittite watar, Sanskrit udrah, Greek hydor, Old Church Slavonic and Russian voda, Lithuanian vanduo, Old Prussian wundan, Gaelic uisge "water;" Latin unda "wave;" Old English wæter, Old High German wazzar, Gothic wato "water."
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undulant (adj.)
1830, from Latin undulantem (nominative undulans), from unda "a wave," from PIE *unda-, nasalized form of root *wed- (1) "water; wet."
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undulation (n.)
1640s, from Medieval Latin *undulatio, from Late Latin undulatus "wavy, undulated," from undula "wavelet," diminutive of Latin unda "a wave," from PIE *unda-, nasalized form of root *wed- (1) "water; wet."
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hydro- 
before vowels hydr-, word-forming element in compounds of Greek origin, meaning "water," from Greek hydro-, combining form of hydor "water" (from suffixed form of PIE root *wed- (1) "water; wet"). Also sometimes a combining form of hydrogen.
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hydrant (n.)
"apparatus for drawing water from a street main," 1806, from Greek hydr-, stem of hydor "water" (from suffixed form of PIE root *wed- (1) "water; wet") + -ant. OED double-damns it as "Irregularly formed" and "of U.S. origin."
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wedlock (n.)
Old English wedlac "pledge-giving, marriage vow," from wed + -lac, noun suffix meaning "actions or proceedings, practice," attested in about a dozen Old English compounds (feohtlac "warfare"), but this is the only surviving example. Suffix altered by folk etymology through association with lock (n.1). Meaning "condition of being married" is recorded from early 13c.
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vodka (n.)

1800, as a Russian word in English, in a description of late 18th century Russian life where it is described as "rectified corn-spirits;" from Russian vodka, literally "little water," diminutive of voda "water" (from PIE *woda-, suffixed form of root *wed- (1) "water; wet") + diminutive suffix -ka.

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anhydrous (adj.)
"containing no water," 1809, a modern coinage from Greek an- "not, without" (see an- (1)) + hydor "water" (from PIE root *wed- (1) "water; wet") + -ous. Greek did have anhydros "waterless," used of arid lands or corpses that had not been given proper funeral rites.
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