fecund (adj.)

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 PIE root *dhe(i)- "to suck, suckle," with derivatives meaning also "produce, yield."

Also from the same Latin root come felare "to suck;" femina "woman" (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."