late 14c., "pleasing to the sight, fair," from Latin speciosus "good-looking, beautiful, fair," also "showy, pretended, plausible, specious," from species "appearance, form, figure, beauty" (see species). Meaning "seemingly desirable, reasonable or probable, but not really so; superficially fair, just, or correct" in English is first recorded 1610s. Related: Speciously; speciosity; speciousness.
Specious is superficially fair, just, or correct, appearing well at first view but easily proved unsound. Plausible is applied to that which pleases the ear or the superficial judgment, but will not bear severe examination. [Century Dictionary, 1895]
updated on October 06, 2019