cucking stool (n.)youdaoicibaDictYouDict[cucking stool 词源字典]
early 13c., from cuck "to void excrement," from Old Norse kuka "feces" (the chair was sometimes in the form of a close-stool). Also known as trebucket and castigatory, it was used on disorderly women and fraudulent tradesmen, either in the form of public exposure to ridicule or for ducking in a pond.[cucking stool etymology, cucking stool origin, 英语词源]
duck (v.)youdaoicibaDictYouDict
"to plunge into" (transitive), c. 1300; to suddenly go under water (intransitive), mid-14c., from presumed Old English *ducan "to duck," found only in derivative duce (n.) "duck" (but there are cognate words in other Germanic languages, such as Old High German tuhhan "to dip," German tauchen "to dive," Old Frisian duka, Middle Dutch duken "to dip, dive," Dutch duiken), from Proto-Germanic *dukjan.

Sense of "bend, stoop quickly" is first recorded in English 1520s. Related: Ducked; ducking. The noun is attested from 1550s in the sense of "quick stoop;" meaning "a plunge, dip" is from 1843.