Pond

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Middle English: alteration of pound3, commonly used in dialect in the same sense.

wiktionary

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From Middle English pond, ponde(“pond, pool”), probably from Old English *pond, *pand (attested in placenames), a variant of pund(“enclosure”). Doublet of pound.

Clipping of  ponder. 

etymonline

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pond (n.)

c. 1300 (by mid-13c. in compounds, c. 1200 in surnames, possibly in Old English), "artificially banked body of water," variant of pound "enclosed place" (for livestock, etc.; see pound (n.2)). Applied locally to natural pools and small lakes from late 15c. Jocular use in reference to the Atlantic Ocean dates from 1640s. Pond scum "free-floating freshwater algae" (Spirogyra) is from 1864 (also called frog-spittle and brook-silk; as figurative for "someone extremely repulsive," it is attested from 1984.