Learn English – Origin of the phrase “sow wild oats”

Courage is reckoned the greatest of all virtues; because, unless a man has that virtue, he has no security for preserving any other.

Samuel Johnson, quote provided by Vincent McNabb in the comments.

Courage is not simply one of the virtues, but the form of every virtue at the testing point.

C.S. Lewis, sourced on Wikiquote.

To my mind, at the testing point implies a test. There's no test if you don't feel fear. I like the M-W definition you give. Note, though, that the Cambridge dictionary says that bravery is defined by not showing fear. It says nothing about not experiencing fear.

Off the top of my head, I'll say that both a brave person and a courageous person may experience fear. The brave person won't show the fear; the courageous person might. The brave are, then, a subset of the courageous. Take that with a grain of salt: I just made it up, but it sounds roughly right to me.

The word used in the situations you described is (transliterated) yada, which simply means "to know" and is often translated (in different circumstances) find, understand, comprehend and acknowledge.

Considering some of the situations presented in the Old Testament (drunken incest of Lot and his daughters, rape of Dinah, rather suggestive imagery in Song of Solomon, etc), I doubt euphemisms would even be considered necessary; however, Strong's concordance suggests it is used euphemistically (in addition to other senses) in the Hebrew.

I imagine those who translated earlier (KJV) would not have seen reason to translate yada any differently when it referred to sex (they rarely translated words differently solely for the sake of clarity), whereas newer translations (NASB), more for the sake of clarity than anything, use another euphemism (ie. had relations with). I doubt any translators would find a reason to change a euphemism in the original language into something more graphic.