Definition of "preposterous"

[...] I did incounter that obſeene and moſt prepoſterous euent that draweth frõ my ſnowhite pen the ebon coloured Incke, which here thou vieweſt, beholdeſt, ſuruayeſt, or ſeeſt. [...] There did I ſee that low ſpirited Swaine, [...] hight Coſtard, (Clow[ne]. O mee) ſorted and conſorted contrary to thy eſtabliſhed proclaymed Edict and continent Cannon; Which with, o with, but with this I paſſion to ſay wherewith: / Clo[wne]. With a Wench.

c. 1595–1596 (date written), W. Shakespere [i.e., William Shakespeare], A Pleasant Conceited Comedie Called, Loues Labors Lost. […] (First Quarto), London: […] W[illiam] W[hite] for Cut[h]bert Burby, published 1598; republished as Shakspere’s Loves Labours Lost (Shakspere-Quarto Facsimiles; no. 5), London: W[illiam] Griggs, […], [Act I, scene i]

So I am to send Mrs. Churchill down to the very spot where a treasonable correspondence is most easily managed; and by the ease with which she gets out of a first scrape, give her all possible encouragement to get into another. Well, I was quite right in asking what preposterous request had you come here about!

1837, L[etitia] E[lizabeth] L[andon], “An Audience”, in Ethel Churchill: Or, The Two Brides. […], volume II, London: Henry Colburn, […], page 257

In the case of the misseltoe, which draws its nourishment from certain trees, which has seeds that must be transported by certain birds, and which has flowers with separate sexes absolutely requiring the agency of certain insects to bring pollen from one flower to the other, it is equally preposterous to account for the structure of this parasite, with its relations to several distinct organic beings, by the effects of external conditions, or of habit, or of the volition of the plant itself.

1859 November 24, Charles Darwin, “Introduction”, in On the Origin of Species by Means of Natural Selection, […], London: John Murray, […]

The preposterous altruism too! If a man takes your coat, give him your cloak. Resist not evil. It is an insane immolation of self—as bad intrinsically as fakirs stabbing themselves or anchorites warping their spines in caves scarcely large enough for a fair-sized dog.

1918, W[illiam] B[abington] Maxwell, chapter XXXIV, in The Mirror and the Lamp, Indianapolis, Ind.: The Bobbs-Merrill Company, page 266

Leading the attack on the president's very citizenship is the professional vulgarian Donald Trump, who gets away with the kind of preposterous, race-based comments granted few black public figures.

2014 December 4, Timothy Egan, “A deficit of dignity”, in The New York Times‎

Democrats, too, must be criticised. While they have not made preposterous statements or been threatening or demagogic, they, all too often, have come up short, failing to propose new ideas that can help unwind conflicts raging across the Middle East.

2016 January 30, “America deserves more from presidential hopefuls”, in The National, retrieved 31 January 2016