Latinate-- words derived from Latin (like 'derive') and not Anglo-Saxon (like 'word'). Jargon is almost always Latinate-- maximize, vitalize, deploy, concept.

Da-tai (= 'da' form) is the short form of verbs- eg, iru, iku, taberu. So called because that form of desu is da. It's an intimate non-polite form-- not rude, but not the one you use with superiors or strangers. That's desu-masu tai, the desu-masu form. Which are desu and imasu, ikimasu, tabemasu, and so on.

And desu, as even the fangirls know, is 'is'. (The 'A = B' is, used to say one thing is another. There's another form for saying something exists.)

But of course intimacy is the wrong word. English doesn't think about the degree of closeness between two speakers, much less their relative social positions, and so lacks vocabulary to express those concepts in languages that think of nothing else. Da-tai says 'we are friends' except when it says 'I outrank you'; and I fancy it's the latter sense that Goujun uses it in

Robertson Davies' Plain Style, I fancy, is what Goujun is. Which one must still keep apart from flat and/or colloquial. Though what to do with those ze's and zo's and kiden's, I wonder.

*laughs* - sorry for the jump in.

Also whilst I'm here (I do this quite a bit) - Very best wishes for a wonderful New Year ahead.