I'm continuing to go over the email questions I received in my absence, and today I'll answer a question about the word hagun הגון. Before I get to the etymology, I'd like to compare hagun with the very simliar word hogen הוגן.
They both can mean "worthy", "proper" or "suitable". However there is a difference between them. Hagun has more of a connotation of "appropriate", whereas hogen is more synonymous with "just" or "fair". (In fact, Israelis will often say the more slangy ze lo fair זה לא פייר , but when they want to be formal, they'll substitute ze lo hogen זה לא הוגן - "that's not fair".) Hagun is usually used for a person who acts appropriately (although it can also be used for other things), but hogen is never used for people, only more abstract things like situations, salaries or verdicts.
Klein points out that both words derive from the root הגן - hogen is the active form and hagun is the passive form, although in the original Talmudic usage there wasn't a difference in meaning between them. Both meant worthy, and we can see that they were interchangeable from such examples as this one from Avot DeRabbi Natan 23:4 - שהיא הוגנת לו, הוא הגון לה - "she is suitable [hogenet] for him, and he is suitable [hagun] for her".
As far as the root of הגן, Klein provides the following etymology (which clearly has somewhat of a sordid past):
Related to Arab. hajuna (= was white), hijan (=white race), hajin (=descendant of a father of noble birth and a woman slave; the best of its kind; excellent), hajinah (=dromedary), JAram הוגנא (= young camel). Krauss and several other scholars dervie הגן from Gk. eugenes (=well born)
And the Online Etymology Dictionary explains the origin of eugenes:
"well-born, of good stock, of noble race," from eu- "good" + genos "birth"
One misconception I found online was that the words hogen and hagun are related to the word for logic, higayon הגיון. That word has gone through some major jumps in its history. In biblical Hebrew, it referred to music, song or other vocal expression (often prayer). It could also mean musing or meditation. In Talmudic Hebrew it came to mean reading, and only in Medieval Hebrew did the meaning of "logic" arrive. The root of higayon is הגה, and Klein says the original meaning was "to hum, murmur, ponder", and that the verb was used to describe the cooing of a pigeon or the growling of a lion. He writes that the origin was probably imitative -i.e. that was the sound those animals made. Later, in post-biblical Hebrew the verb also began to referring to pronouncing, spelling and editing words.
In this fascinating Hebrew article, Rabbi Yoel Bin Nun bemoans the transformation of higayon from song to logic (he says the same phenomenon applied to the root שכל). He puts the onus for this change on the Rambam, saying in doing so he made our focus on God much more sterile, intellectual and philosophical, and abandoned the traditional emphasis on faith and prayer. I'll leave it up to you if that is a hagun or a hogen conclusion...