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."