I looked this up.
hay (n.) "grass mown," Old English
heg (Anglian),
hieg,
hig (West Saxon) "grass cut or mown for fodder," from Proto-Germanic
*haujam (cognates: Old Norse
hey, Old Frisian
ha, Middle Dutch
hoy, German
Heu, Gothic
hawi "hay"), literally "that which is cut," or "that which can be mowed," from PIE
*kau- "to hew, strike" (cognates: Old English
heawan "to cut;" see
hew).
hew (v.) Old English
heawan "to chop, hack, gash, strike with a cutting weapon or tool" (class VII strong verb; past tense
heow, past participle
heawen), earlier
geheawan, from Proto-Germanic
*hawwan (cognates: Old Norse
hoggva, Old Frisian
hawa, Old Saxon
hauwan, Middle Dutch
hauwen, Dutch
houwen, Old High German
houwan, German
hauen "to cut, strike, hew"), from PIE
*kau- "to hew, strike," a root more widely developed in Slavic (cognates: Old Church Slavonic
kovo, Lithuanian
kauti "to strike, beat, fight;" Polish
kúc "to forge," Russian
kovat' "to strike, hammer, forge;" Latin
cudere "to strike, beat;" Middle Irish
cuad "beat, fight").
fennel (n.) Old English
fenol,
finul,
finol "fennel," perhaps via (or influenced by) Old French
fenoil (13c.) or directly from Vulgar Latin
*fenuculum, from Latin
feniculum/
faeniculum, diminutive of
fenum/
faenum "hay," probably literally "produce" (see
fecund). Apparently so called from its hay-like appearance and sweet odor. 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."