Specious (adjective)

1. Seeming true or reasonable but in fact fallacious or misleading.
2. Deceptively attractive; superficially plausible.

Origin:

From latin speciōsus ("showy, beautiful"), from species ("appearanc.e")

Examples:

1. The argument was specious and didn't hold up to scrutiny.
2. The politician's specious reasoning was exposed as flawed.
3. The specious explanation didn't convince anyone.
4. The specious theory was quickly debunked by experts.
5. The specious advertisements promised quick and easy weight loss.