Dictionaries are good for providing lots of definitions for the same word. Philosophers prefer for each word they use to mean one specific thing. So what philosophers mean by 'valid' and what you or I mean by 'valid' in casual conversation can be two different things.
If you don't trust the one source I provided on what philosophers mean by 'valid', then how about these:
Truth, Validity, and Soundness
Univ of Idaho on Validity and Soundness
Montana weighs in on Validity and Soundness
...and there are dozens of other links.
I've read and agreed with numerous posts you have made on other threads. I thought for sure you knew the difference between valid and sound arguments. There are others on FR who spend too much time underestimating the intelligence of the liberal opposition. Not all liberals are idiots. They are just imperfect humans who have chosen bad premises from which to start. I think that is why it is so difficult to change peoples' minds and why so much political and social argumentation is talking past each other. Since we don't start out from the same premises, any amount of logic or reason doesn't help end the debate. It's why everyone wants to get to kids when they're young in order to shape their minds in a specific way, to fix the premises early and make them as unshakable as possible.