1540s, "the expulsion of the fetus before it is viable," originally of deliberate as well as unintended miscarriages; from Latin abortionem (nominative abortio) "miscarriage; abortion, procuring of an untimely birth," noun of action from past-participle stem of aboriri "to miscarry, be aborted, fail, disappear, pass away," a compound word used in Latin for deaths, miscarriages, sunsets, etc., which according to OED is from ab, here as "amiss" (see ab-), + stem of oriri "appear, be born, arise" (see origin).
Meaning "product of an untimely birth" is from 1630s; earlier in this sense was abortive (early 14c.). Another earlier noun in English for "miscarriage" was abort (early 15c.). In the Middle English translation of Guy de Chauliac's "Grande Chirurgie" (early 15c.) Latin aborsum is used for "stillbirth, forced abortion." Abortment is attested from c. 1600; aborsement from 1530s, both archaic. Aborticide (1875) is illogical. Compare miscarriage.
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). The deliberate miscarriage was criminal abortion. This broke down late 19c. as abortion came to be used principally for intentional miscarriages, probably via phrases such as procure an abortion.
Criminal abortion is premeditated or intentional abortion procured, at any of pregnancy, by artificial means, and solely for the purpose of preventing the birth of a living child : feticide. At common law the criminality depended on the abortion being caused after quickening. [Century Dictionary, 1899]
Foeticide (n.) appears 1823 as a forensic medical term for deliberate premature fatal expulsion of the fetus; also compare prolicide. Another 19c. medical term for it was embryoctony, with second element from a Latinized form of Greek kteinein "to destroy." 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. Abortium "hospital specializing in abortions," is from 1934, in a Soviet Union context.