Etymological question - why do words like debar and bar and depress and press mean the same things?

Good question. It happens a lot in English. There are also flammable and inflammable.

Linguists call prefixes used for this purpose “intensifiers” because they’re meant to emphasize the verb rather than to change its meaning. Other prefixes used this way include:

“con-” in condemn
“com-” in commend
“de-” in deprive, desiccate
“im-” in imminent, impinge, impress
“ob-” in obdurate, oblige, obtain
“pro-” in promiscuous, prominent

I am not sure that it’s quite the same…I am looking specifically at words that can stand by themselves without the prefix. like if your list were these, promiscuous and miscuous would both mean the same things.

Back when the intensifiers were added, they were added to stand-alone words. Over time, some of those original root words have survived in English vocabulary, others haven’t. “depress” evolved from de + pressare. It just so happens that both the root and the intensified version are still in use.

gotcha….can I start mending people for advancement? or riving my son of television when he misbehaves? and taining a raise for a positive performance evaluation?

LOL Thanks!

Studying English is, to badly paraphrase and misquote Robert Frost, like “playing tennis without a net.”
Or maybe with two nets. And three balls.
And a kosher dill for a racquet.
But that’s why it’s so much fun!