Etymology
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sound (n.2)
"narrow channel of water," c. 1300, from Old Norse sund "a strait, swimming," or from cognate Old English sund "act of swimming, stretch of water one can swim across, a strait of the sea," both from Proto-Germanic *sundam-, from *swum-to-, suffixed form of Germanic root *swem- "to move, stir, swim" (see swim (v.)).
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sound (v.2)
"fathom, probe, measure the depth of," mid-14c. (implied in sounding), from Old French sonder, from sonde "sounding line," perhaps from the same Germanic source that yielded Old English sund "water, sea" (see sound (n.2)). Barnhart dismisses the old theory that it is from Latin subundare. Figurative use from 1570s.
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sound (adj.)
"free from special defect or injury," c. 1200, from Old English gesund "sound, safe, having the organs and faculties complete and in perfect action," from Proto-Germanic *sunda-, from Germanic root *swen-to- "healthy, strong" (source also of Old Saxon gisund, Old Frisian sund, Dutch gezond, Old High German gisunt, German gesund "healthy," as in the post-sneezing interjection gesundheit; also Old English swið "strong," Gothic swinþs "strong," German geschwind "fast, quick"), with connections in Indo-Iranian and Balto-Slavic. Meaning "right, correct, free from error" is from mid-15c. Meaning "financially solid or safe" is attested from c. 1600; of sleep, "undisturbed," from 1540s. Sense of "holding accepted opinions" is from 1520s.
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Sunday (n.)

first day of the week, Old English sunnandæg (Northumbrian sunnadæg), literally "day of the sun," from sunnan, oblique case of sunne "sun" (see sun (n.)) + dæg "day" (see day). A Germanic loan-translation of Latin dies solis "day of the sun," which is itself a loan-translation of Greek hēmera heliou. Compare Old Saxon sunnun dag, Old Frisian sunnandei, Old Norse sunnundagr, Dutch zondag, German Sonntag "Sunday."

In European Christian cultures outside Germanic often with a name meaning "the Lord's Day" (Latin Dominica). Sunday-school dates from 1783 (originally for secular instruction); Sunday clothes is from 1640s. Sunday driver is from 1925.

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sundry (adj.)
Old English syndrig "separate, apart, special, various, distinct, characteristic," from sundor "separately, apart, asunder" (see sunder) + -y (2). Compare Old High German suntaric, Swedish söndrig "broken, tattered." Meaning "several" is from 1375. As a noun, from mid-13c. with the sense "various ones." Phrase all and sundry is from late 14c.
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sundog (n.)
"mock sun, parhelion," 1650s; the second element is of obscure origin.
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sundial (n.)
also sun-dial, 1590s, from sun (n.) + dial (n.). Earlier simply dial.
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sunder (v.)
Old English sundrian, syndrian "to sunder, separate, divide," from sundor "separately, apart," from Proto-Germanic *sunder (source also of Old Norse sundr, Old Frisian sunder, Old High German suntar "aside, apart;" German sondern "to separate"), from PIE root *sen(e)- "apart, separated" (source also of Sanskrit sanutar "away, aside," Avestan hanare "without," Greek ater "without," Latin sine "without," Old Church Slavonic svene "without," Old Irish sain "different"). Related: Sundered; sundering.
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sundries (n.)
"various small things," 1755, plural of sundry (adj.) used as a noun. "[A] comprehensive term used for brevity, especially in accounts" [Century Dictionary].
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sundae (n.)
1897, American English, thought to be an alteration of Sunday, perhaps re-spelled in deference to religious feelings; but the reason for the name is uncertain; perhaps "ice cream left over from Sunday, on sale later." For a fuller account of the speculations, see H.L. Mencken, "The American Language," Supplement I (1945), pp.376-7.
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