fecund (adj.)youdaoicibaDictYouDict[fecund 词源字典]
a 16c. Latinizing revision of the spelling of Middle English fecond (early 15c.), from Middle French fecond (Old French fecont "fruitful"), from Latin fecundus "fruitful, fertile, productive; rich, abundant," from *fe-kwondo-, suffixed form (adjectival) of Latin root *fe-, corresponding to PIE *dhe(i)- "to suck, suckle," also "produce, yield."

Cognates include: Sanskrit dhayati "sucks," dhayah "nourishing;" Greek thele "mother's breast, nipple," thelys "female, fruitful;" Old Church Slavonic dojiti "to suckle," dojilica "nurse," deti "child;" Lithuanian dele "leech;" Old Prussian dadan "milk;" Gothic daddjan "to suckle;" Old Swedish dia "suckle;" Old High German tila "female breast;" Old Irish denaim "I suck," dinu "lamb."

Also from the same Latin root come felare "to suck;" femina "woman" (*fe-mna-, literally "she who suckles"); felix "happy, auspicious, fruitful;" fetus "offspring, pregnancy;" fenum "hay" (probably literally "produce"); and probably filia/filius "daughter/son," assimilated from *felios, originally "a suckling."[fecund etymology, fecund origin, 英语词源]
suck (v.)youdaoicibaDictYouDict
Old English sucan "to suck," from a Germanic root of imitative origin (cognates: Old Saxon, Old High German sugan, Old Norse suga, Danish suge, Swedish suga, Middle Dutch sughen, Dutch zuigen, German saugen "to suck"), possibly from the same source as Latin sugere "to suck," succus "juice, sap;" Old Irish sugim, Welsh sugno "to suck;" see sup (v.2). As a noun from c. 1300.

Meaning "do fellatio" is first recorded 1928. Slang sense of "be contemptible" first attested 1971 (the underlying notion is of fellatio). Related: Sucked; sucking. Suck eggs is from 1906. Suck hind tit "be inferior" is American English slang first recorded 1940.
The old, old saying that the runt pig always sucks the hind teat is not so far wrong, as it quite approximates the condition that exists. ["The Chester White Journal," April 1921]
weasel (v.)youdaoicibaDictYouDict
"to deprive (a word or phrase) of its meaning," 1900, from weasel (n.); so used because the weasel sucks out the contents of eggs, leaving the shell intact. Both this and weasel-word are first attested in "The Stained-Glass Political Platform," a short story by Stewart Chaplin, first printed in "Century Magazine," June 1900:
"Why, weasel words are words that suck all the life out of the words next to them, just as a weasel sucks an egg and leaves the shell. If you heft the egg afterward it's as light as a feather, and not very filling when you're hungry; but a basketful of them would make quite a show, and would bamboozle the unwary."
They were picked up at once in American political slang. The sense of "extricate oneself (from a difficult place) like a weasel" is first recorded 1925; that of "to evade and equivocate" is from 1956. Related: Weasled; weasling.