specious

Etymology 1

From Latin speciōsus (“good-looking”).

adj

1. Seemingly well-reasoned, plausible or true, but actually fallacious.
   This idea that we must see through what we have started is specious, however good it may sound.
   I have frequently amused myself both in public and private companies, with silently remarking, the specious errors of those who speak without reflecting. 1776, Thomas Paine, Common Sense
   “Number two is that for reasons which I regarded at the time as specious and insulting, the Americans objected to your husband's presence on that committee not three weeks after it met, and asked me to replace him with somebody more to their liking. Since Magnus was kingpin of the Czecho operation and of several other little shows in Eastern Europe besides, this was a totally unrealistic demand." 1986, John le Carré, A Perfect Spy
   Feig’s Ghostbusters isn’t out until July 15, but since the project was announced in 2014 as a reboot of the hit 1984 film[…] a vocal minority of movie fans have come up with specious reasons to criticize it. 2016-05-18, David Sims, “The Outcry Against the All-Female ‘Ghostbusters’ Remake Gets Louder”, in The Atlantic
2. Employing fallacious but deceptively plausible arguments; deceitful.
   But a third cause of the delusion is, that the Church of Rome has become more specious and deceitful than before the Reformation. 1829, William Phelan, Mortimer O'Sullivan, “Ireland: A digest taken before Select Committees of the two Houses of Parliament, appointed to inquire into the State of Ireland, 1824—25”, in The Christian Review and Clerical Magazine, volume III, page 472
3. Having an attractive appearance intended to generate a favorable response; deceptively attractive.
   And could any thing be more ſpecious, or more equal, than that fair diſtribution of power and profit, which men called the NEW MODEL? 1760, William Warburton, The Lord Bishop of Gloucester's Sermon Preached Before the Right Honourable the House of Lords, January 30, 1760, page 19
   [T]he success of Trajan, however transient, was rapid and specious. The degenerate Parthians, broken by intestine discord, fled before his arms. 1776, Edward Gibbon, The History of the Decline and Fall of the Roman Empire, Vol I, ch 1-pt i
   This argument, though specious, will not, upon examination, be found solid. 1788, Alexander Hamilton, Federalist No. 59
4. (obsolete) Beautiful, pleasing to look at.

Etymology 2

See speciose.

adj

1. Alternative form of speciose (“rich in species”).
   Coelorinchus is the most specious genus of macrourids with 122 species at the time of writing and more yet to be described. 2017, Imants G. Priede, “Systematic Description of Deep-Sea Fishes”, in Deep-Sea Fishes: Biology, Diversity, Ecology and Fisheries, Cambridge: Cambridge University Press, →DOI, page 216