Synonym of SPECIOUS

Insincere : not expressing genuine feelings.
Sharp : (of an object) having an edge or point that is able to cut or pierce something.
Straight : extending or moving uniformly in one direction only; without a curve or bend.
Frank : open, honest, and direct in speech or writing, especially when dealing with unpalatable matters.
Specious : misleading in appearance, especially misleadingly attractive.

Synonym of Specious is Insincere