Is it ensure, insure, or assure?
plausible but not true; based on pretense; sophistic
Latin specissus 'beautiful, plausible'
c.1400, "pleasing to the sight, fair," from Latin speciosus "good-looking, beautiful," from species "appearance" (see species). Meaning "seemingly desirable, reasonable or probable, but not really so" is first recorded 1610s.