Online Etymology Dictionary

fetus: late 14c., from L. fetus "the bearing, bringing forth, or hatching of young," from L. base *fe- "to generate, bear," also "to suck, suckle" (see fecund). In L., this was sometimes transferred figuratively to the newborn creature itself, or used in a sense of "offspring, brood" (cf. "Germania quos horrida parturit fetus," Horace), but this was not the basic meaning. Also used of plants, in the sense of "fruit, produce, shoot." The spelling foetus is sometimes attempted as a learned Latinism, but it is not historic.
chorion: "outer membrane of the fetus," 1540s, from Gk. khorion "membrane enclosing the fetus, afterbirth," perhaps from PIE *ghere- "gut, entrail."
effete: 1621, from L. effetus (usually in fem. effeta) "unproductive, worn out (with bearing offspring)" lit. "that has given birth," from ex- "out" + fetus "childbearing, offspring" (see fetus). Sense of "exhausted" is 1662; that of "morally exhausted" (1790) led to "decadent" (19c.).
fawn (n.): 1274, from O.Fr. faon "young animal," from V.L. *fetonem, acc. of *feto, from L. fetus "an offspring" (see fetus). Still used of the young of any animal in King James I's private translation of the Psalms, but mainly of deer from 15c. Color use is 1881.
abortion: 1540s, from L. abortionem (nom. abortio) "miscarriage, abortion," from abortus, pp. of aboriri (see abortive). Originally of both deliberate and unintended miscarriages; in 19c. some effort was made to distinguish abortion "expulsion of the fetus between 6 weeks and 6 months" from miscarriage (the same within 6 weeks of conception) and premature labor (delivery after 6 months but before due time). This broke down as abortion came to be used principally for intentional miscarriages. Foeticide (v.) appears 1844 as a medical term for deliberate premature explusion of the fetus. Abortion was a taboo word for much of early 20c., disguised in print as criminal operation (U.S.) or illegal operation (U.K.), and replaced by miscarriage in film versions of novels. Abortionist is recorded by 1872.
amniotic: 1822, from Mod.L. amnion, from Gk., "membrane around a fetus," originally "bowl in which the blood of victims was caught," from ame "bucket."
fetal: formed in English 1811, from fetus + -al (1).
miscarry: mid-14c., "to come to harm, perish;" of persons, "to die," of objects, "to be lost or destroyed," from mis- (1) "wrongly" + caryen "carry" (see carry). Meaning "deliver unviable fetus" first recorded 1520s; that of "fail, come to naught" (of plans or designs) is from c.1600.
foetus: see fetus; for spelling, see oe.
caul: c.1327, "close-fitting cap worn by women," from Fr. cale "cap," back-formation from calotte, from It. callotta, from L. calautica "type of female headdress with pendent lappets," a foreign word of unknown origin. Medical use, in ref. to various membranes, dates to 1382. Esp. of the amnion enclosing the fetus before birth from 1547. This, if the child is born draped in it, was supersititously supposed to protect against drowning (cauls were advertised for sale in British newspapers through WWI).
breed: O.E. bredan "bring young to birth, carry," also "cherish, keep warm," from W.Gmc. *brodjan (cf. O.H.G. bruoten, Ger. brüten "to brood, hatch"), from *brod- "fetus, hatchling," from PIE *bhreue- "burn, heat" (see brood). Original notion of the word was incubation, warming to hatch. Breeding "good manners" is from 1590s.
calf: O.E. cealf (Anglian cælf) "young cow," from W.Gmc. *kalbam (cf. M.Du. calf, O.N. kalfr, Ger. Kalb, Goth. kalbo), perhaps from PIE *gelb(h)-, from base *gel- "to swell," hence, "womb, fetus, young of an animal." Elliptical sense of "leather made from the skin of a calf" is from 1727. Used of icebergs that break off from glaciers from 1818. Calf of the leg (early 14c.) is from O.N. kalfi, source unknown; possibly from the same Germanic root.
brood: O.E. brod "brood, fetus, hatchling," from P.Gmc. *brod (cf. M.Du. broet, O.H.G. bruot, Ger. Brut "brood"), lit. "that which is hatched by heat," from *bro- "to warm, heat," from PIE *bhre- "burn, heat, incubate," from base *bhreue- "to boil, bubble, effervesce, burn" (see brew). The verbal figurative meaning ("to incubate in the mind") is first recorded 1570s, from notion of "nursing" one's anger, resentment, etc. Related: Brooded.
fecund: early 15c., from O.Fr. fecond, from L. fecundus "fruitful, fertile," from *fe-kwondo-, suffixed form of L. base *fe-, corresponding to PIE *dhe(i)- "to suck, suckle," also "produce, yield" (cf. Skt. dhayati "sucks," dhayah "nourishing;" Gk. thele "mother's breast, nipple," thelys "female, fruitful;" O.C.S. dojiti "to suckle," dojilica "nurse," deti "child;" Lith. dele "leech;" O.Prus. dadan "milk;" Goth. daddjan "to suckle;" O.Swed. dia "suckle;" O.H.G. tila "female breast;" O.Ir. denaim "I suck," dinu "lamb"). Also from the same L. base come felare "to suck;" femina "woman" (*fe-mna-, lit. "she who suckles"); felix "happy, auspicious, fruitful;" fetus "offspring, pregnancy;" fenum "hay" (probably lit. "produce"); and probably filia/filius "daughter/son," assimilated from *felios, originally "a suckling."
oe: found in Gk. borrowings into Latin, represtenting Gk. -oi-. Words with -oe- that came early into Eng. from O.Fr. or M.L. usually already had been leveled to -e- (e.g. economic, penal, cemetery), but later borrowings directly from L. or Gk. tended to retain it at first (oestrus, diarrhoea, amoeba) as did proper names (Oedipus, Phoebe, Phoenix) and purely technical terms. British English tends to be more conservative with it than American, which has done away with it in all but a few instances. It also occurred in some native L. words (foedus "treaty, league," foetere "to stink," hence occasionally in Eng. foetid, foederal, which was the form in the original publications of the "Federalist" papers). In these it represents an ancient -oi- in Old Latin (e.g. O.L. oino, Classical L. unus), which apparently passed through an -oe- form before being leveled out but was preserved into Classical L. in certain words, especially those belonging to the realms of law (e.g. foedus) and religion, which, along with the vocabulary of sailors, are the most conservative branches of any language in any time, through a need for precision, immediate comprehension, demonstration of learning, or superstition. But in foetus it was an unetymological spelling in L. that was picked up in Eng. and formed the predominant spelling of fetus into the early 20c.