Etymology
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suckling (n.)
mid-15c., "infant at the breast," from suck + diminutive suffix -ling. Similar formation in Middle Dutch sogeling, Dutch zuigeling, German Säugling. Meaning "calf or other young mammal" is from 1520s. Meaning "act of breast-feeding" is attested from 1799. Adjectival sense "not yet weaned" is from 1799.
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suckle (v.)
c. 1400, perhaps a causative or frequentative form of Middle English suken "to suck" (see suck), but OED suggests instead a back-formation from suckling (though this word is attested only from mid-15c.). Related: Suckled; suckling.
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lactation (n.)

1660s, "process of suckling an infant," from French lactation, from Late Latin lactationem (nominative lactatio) "a suckling," noun of action from past-participle stem of lactare "to suckle," from lac (genitive lactis) "milk" (from PIE root *g(a)lag- "milk"). Meaning "process of secreting milk from the breasts" first recorded 1857. Related: Lactational.

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dug (n.)

"animal nipple," or, contemptuously, "the human female breast," originally with reference to suckling, 1520s, origin obscure, perhaps related to Swedish dagga, Danish dægge "to suckle."

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wean (v.)
"train (an infant or animal) to forego suckling," c. 1200, from Old English wenian "to accustom, habituate," from Proto-Germanic *wanjan (source also of Old Norse venja, Dutch wennen, Old High German giwennan, German gewöhnen "to accustom"), from PIE *won-eyo-, causative form of root *wen- (1) "to desire, strive for."

The sense of "accustom a child to not suckling from the breast" in Old English generally was expressed by gewenian or awenian, which has a sense of "unaccustom" (compare German abgewöhnen, entwöhnen "to wean," literally "to unaccustom"). The modern word might be one of these with the prefix worn off, or it might be wenian in a specialized sense of "accustom to a new diet." Figurative extension to any pursuit or habit is from 1520s.
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filial (adj.)
late 14c., from Late Latin filialis "of a son or daughter," from Latin filius "son," filia "daughter," possibly from a suffixed form of PIE root *bheue- "to be, exist, grow" (see be), but Watkins finds it "more likely" assimilated from *felios, originally "a suckling," a suffixed form of PIE root *dhe(i)- "to suck, suckle."
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nurture (n.)

c. 1300, norture, "upbringing, the act or responsibility of rearing a child," also "breeding, manners, courtesy," from Old French norture, nourreture "food, nourishment; education, training," from Late Latin nutritia "a nursing, suckling," from Latin nutrire "to nourish, suckle" (see nourish). From mid-14c. as "nourishment, food."

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farrow (n.)
Old English fearh "young pig," from Proto-Germanic *farkhaz "young pig" (source also of Middle Low German ferken, Dutch varken, both diminutives; Old High German farh, German Ferkel "young pig, suckling pig," and the second element in aardvark), from PIE root *porko- "young pig." Sense of "a litter of pigs" first recorded 1570s, probably via the verb ("to bring forth piglets," of a sow), which is attested from early 13c.
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nursery (n.)

c. 1300, noricerie, "place or room for infants and young children and their nurse," from Old French norture, norreture "food, nourishment; education, training," from Late Latin nutritia "a nursing, suckling," from Latin nutrire "to nourish, suckle" (see nourish). From c. 1500 as "place where anything is fostered." As a type of school for very young children, 1580s. The horticultural sense of "place where trees are raised to be transplanted" is from 1560s. Nursery rhyme is by 1807.

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fecund (adj.)

a 16c. Latinizing revision of the spelling of Middle English fecond, fecound (early 15c.), from Old French fecond, fecont "fruitful" and directly 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."

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