Synonyms for Specious (same or very similar meaning)
WordNet sense 1 (plausible but false):
spuriousWordNet sense 2 (not in accordance with the fact or reality or actuality):
falseWordNet sense 3 (based on pretense; deceptively pleasing):
meretricious, gildedWordNet sense 4 (lacking sincerity):
insincereFrom the ODE community, based on WordNetadd/edit