From the second edition (1989):
(əˈbɔːʃən) Also 6 abhorsion. [ad. L. abortiōn-em n. of action f. aborī-ri: see abort.]

1. The act of giving untimely birth to offspring, premature delivery, miscarriage; the procuring of premature delivery so as to destroy offspring. (In Med. abortion is limited to a delivery so premature that the offspring cannot live, i.e. in the case of the human fœtus before the sixth month.)

1547 Boorde Brev. Health iii. 8 Abhorsion is when a woman is delyvered of her chylde before her tyme. 1646 Sir T. Browne Pseud. Ep. 67 Physitions‥promise therein a vertue against abortion. 1778 Robertson America I. iv. 297 The women by the use of certain herbs procure frequent abortions. 1869 Lecky Europ. Morals II. i. 22 The practice of abortion was one to which few persons in antiquity attached any deep feeling of condemnation.

b. fig. Failure (of aim or promise).

1710 in Somers Tracts I. 10 All the Fruit of his Labour ends in Sterility and Abortion. 1797 Godwin Enquirer i. v. 35 Genius [may] terminate in an abortion. 1814 F. Burney Wanderer IV. 58 The abortion of my purpose may have made me appear a mere female mountebank.

2. Biol. Arrestment of development of any organ, so that it either remains a mere rudiment, or is entirely shrivelled up or absorbed.

1842 A. Gray Struct. Bot. (1880) vi. §3. 179 Non-appearance of some parts which are supposed in the type = Abortion or Suppression. 1859 Darwin Orig. Spec. (1873) v. 116 The partial or complete abortion of the reproductive organs. 1870 Rolleston An. Life 25 The skull of the Common Fowl differs in the abortion of the posterior crus.

3. The imperfect offspring of an untimely birth, or any dwarfed and misshapen product of generation; hence fig. the nugatory or empty result of any action.

1640 Bp. Hall Christ. Mod. (Ward) 15/1 Those bodily delights‥alas! what poor abortions they are, dead in the very conception. 1858 Hawthorne Fr. & It. Journ. I. 171 A little abortion of a man‥hastened before us. 1872 O. W. Holmes Poet Breakf. Tab. x. 315 The doctrine of man's being a blighted abortion, a miserable disappointment to his Creator. 1878 H. M. Stanley Dark. Cont. II. iii. 74 His feet are monstrous abortions.