Having the ring of truth or plausibility but actually fallacious: a specious argument.
Deceptively attractive.
[Middle English, attractive, from Latin speciōsus, from speciēs, appearance; see spek- in Indo-European roots.] spe'cious·ly adv., spe'ci·os'i·ty (-shē-ŏs'ĭ-tē), spe'cious·ness (-shəs-nĭs) n.
c.1400, "pleasing to the sight, fair," from L. speciosus "good-looking, beautiful," from species "appearance" (see species). Meaning "seemingly desirable, reasonable or probable, but not really so" is first recorded 1612.